# Baking sheets, mats and liners: research notes

Date: 2026-10-25. Scope: flat oven sheets (rimmed sheet pans, jelly roll pans, rimless cookie sheets, insulated sheets, broiler pans, toaster-oven sheets, sheet-and-rack sets), reusable silicone baking mats, parchment sold for lining pans (rolls and pre-cut sheets), and oven liners that catch drips; not cake, loaf, pizza or casserole pans (sibling `baking-pans`), not stand-alone cooling racks (sibling `kitchen-boards`), not cooking bags (sibling `oven-mitts`), not foil or food wraps.

Overlaps with siblings, left to them: a wire rack sold alone belongs to `kitchen-boards` ("Cutting Boards, Cooling Racks & Prep Surfaces"); a pizza pan or perforated pizza tray belongs to `baking-pans` ("Baking Pans, Pizza Stones & Ovenware"). Sheet-plus-rack sets stay here because the Amazon query map sends "baking sheet with rack" to this leaf (`zamana-expertise/archive/amazon-queries/kitchen-and-dining-amazon-queries.csv`, lines 725 to 743, which also send "oven liner" and "broiler pan" here). Parchment and foil have no explicit leaf; parchment is kept here because it is the archetypal pan liner and the reviewers compare it directly with mats; foil is left out because it is a general wrap.

Quote labels: **verbatim** = the sentence was read in raw page text (curl plus tag stripping, or pdftotext) and is quoted exactly; **fetched excerpt** = summarised from a fetched page; **search excerpt** = seen only in a search-engine summary. No number in category.json rests on a search excerpt. Every page below except where marked was read as raw text saved under the scratchpad folder `baking-sheets/`.

## Seed

Seed output, verbatim:

```
=== Example entry (from an unrelated category) ===
category: car-tyres
what this shows: a number that is on every listing and still needs a judgement attached, because experts know it only compares within one manufacturer's range.

<example>
{
  "id": "treadwear_grade",
  "label": "Treadwear grade",
  "definition": "A number moulded on the tyre's side, from a US test, that estimates how long the tread lasts relative to a reference tyre set at 100.",
  "why_experts_care": "A 600 should last roughly twice as long as a 300, which is the single biggest driver of cost per mile. The catch experts repeat is that each manufacturer runs its own test, so the number is reliable for comparing tyres within one brand and loose across brands. Softer, grippier tyres sit low on this scale on purpose.",
  "kind": "numeric",
  "unit": "grade",
  "range": { "min": 60, "max": 1000, "typical": "Most everyday tyres sit between 300 and 700." },
  "roles": ["annotation", "sort_key"],
  "novice_answerable": false,
  "source": "listing",
  "listing_field_hint": "Listed as UTQG, usually as three values together, for example 500 A A. Treadwear is the first.",
  "backfill_cost": "low",
  "backfill_note": "If absent from the listing, the manufacturer's spec sheet always has it.",
  "visual": { "chartable": true, "encoding": "position on a horizontal scale, with the grip grade as a second mark so the trade-off shows" },
  "priority": { "narrows_set": 3, "cost_to_answer": 3 },
  "evidence": ["nhtsa_utqg", "tirerack_explainer"]
}
</example>

Judgement that would accompany it:
{
  "claim": "Treadwear grades can be compared across brands as a rough guide but not as a ranking.",
  "confidence": "high",
  "sources_disagree": true,
  "note": "The regulator describes the test as standard. Specialist reviewers say manufacturers calibrate differently. We side with the reviewers because they test the tyres."
}

=== Persona ===
A perfumer, who thinks in what you notice first, what lasts, and what fades

Ask yourself two things and write the answers under 'Seed' in notes.md:
  1. What is the baking-sheets equivalent of the example above?
  2. What would this persona notice first about baking-sheets that a typical buyer would not?
Keep what survives the data check. Drop the rest.
```

1. The baking-sheet equivalent of treadwear is the metal gauge. It is a number on commercial spec sheets (Vollrath lists "Gauge 18", "16", "13", "12"), buyers read it as "heavier is better", and it needs a judgement attached: the number runs backwards (a smaller gauge is thicker metal) and it means different thicknesses in different metals (18 gauge is 0.0403 in aluminum and 0.0478 in steel in both tables read). So gauge compares within one metal and is loose across metals, which is the treadwear shape exactly. Survived as `metal_thickness`, the `thickness_mm` metric and a judgement. One wrinkle kept in notes only: Vollrath's own site lists the standard-duty nonstick 5303NS and the heavy-duty natural 5303 both as "Gauge 18", with case weights of 13 lb and 23.6 lb per 12 pans; that may be a site data error, so it is not in the JSON.
2. A perfumer notices what changes over time. First impression: a shiny new aluminum pan. What lasts: ATK's test says the pan that has darkened with use browns better, so the patina is a feature, not wear. What fades: nonstick coatings wear out (ATK: "All types of nonstick coating wear away with time"), and silicone mats absorb oils and odours (ATK mats review). Survived as `surface_color`, a judgement, and two trade-offs. Dropped: a years-of-life figure for nonstick coatings (no source gives one), Silpat's "over 2,000 times" use claim as a number (the maker's own figure, single source), and first-impression shine as a facet (it is the photo, and ATK says it does not matter).

## Sources and what each supports

### Specialist reviewers who test

**America's Test Kitchen, The Best Rimmed Baking Sheets of 2026** https://www.americastestkitchen.com/equipment_reviews/1718-rimmed-baking-sheets (`atk_rimmed`)
- verbatim: "Full-size baking sheets can be found in professional kitchens and bakeries but won't fit in home ovens."
- verbatim: "You'll usually see the dimensions of a half-sheet pan listed as 18 by 13 inches, but in practice, the actual cooking surfaces measure closer to 16½ by 11½ inches."
- verbatim: "Quarter-sheet pans, with a cooking surface measuring about 8½ by 11½ inches, and eighth-sheet pans, with a cooking surface of about 8¾ by 5½ inches".
- verbatim: aluminum sheets are "notoriously prone to warping", and "cooking acidic ingredients, such as tomatoes or vinegar, in uncoated aluminum can cause the metal to leach into food. Nonstick baking sheets ... can't be used at temperatures higher than 450 degrees or under the broiler".
- verbatim: "Cladding makes stainless-steel models weigh more than twice as much as a typical aluminum baking sheet: 3 to 4.5 pounds versus about 1.5 pounds."
- verbatim: "the cooking surfaces of the stainless-steel half sheets we tested were almost all significantly larger or smaller than the 16½ by 11½-inch dimensions"; "you'll need to buy a rack made by the pan's manufacturer".
- verbatim: "In our experience, baking sheets are most likely to warp when preheated empty at high temperatures ... In most cases, the warping isn't permanent".
- verbatim: "we preferred half-sheet baking pans that weighed under 2 pounds"; "straighter, smooth sides that were at least 1 inch tall".
- verbatim: "Aluminum baking sheets should not go in the dishwasher because uncoated aluminum reacts with harsh detergents".
- verbatim: aluminum-coated steel pan: "This aluminum-coated steel sheet matched the performance of the all-aluminum models."
- verbatim: big-batch version "Its walls are 2 inches tall instead of just 1 inch."
- verbatim: stainless "tend to brown food slightly more quickly".
- Confidence high.

**ATK, The Best Cookie Sheets** https://www.americastestkitchen.com/equipment_reviews/2749-the-best-cookie-sheets (`atk_cookie`)
- verbatim: "Rimmed baking sheets typically have a 1-inch rim around all four sides, while cookie sheets usually have only one or two lower raised edges."
- verbatim: "The lack of rims also means air circulates around a cookie sheet better ... This increase in airflow can slightly speed up baking time."
- verbatim: rimmed sheets "often darken and dull over time ... it can potentially cause cookies to overbake".
- verbatim: "Thick metal promotes even baking and resists warping. Our favorite cookie sheets were one layer of aluminum or steel and ranged in thickness from almost 1 millimeter to roughly 2.5 millimeters." (the mm range is single-source, kept in notes only)
- verbatim: "Those with around 200 square inches of usable baking space were roomy without being unwieldy" (single source; notes only).
- verbatim on insulated: "They produced unevenly browned cookies"; "cookies ... spread before they set"; "They warped during use"; one "insulated sheet warped at a modest 350 degrees" (number kept in notes only).
- verbatim: "nonstick coatings break down over time and the sheets need to be replaced."
- verbatim: a dark sheet: "Its dark surface caused the cookies to brown significantly more than cookies baked on lighter sheets".
- verbatim: "A standard sheet of parchment (16½ x 12¼ in)".
- verbatim: cookie sheets weighing "about 3 pounds or more were hard to handle comfortably"; the stainless-clad sheet "weighing about 4 pounds".
- Confidence high.

**ATK, The Best Nonstick Rimmed Baking Sheets** https://www.americastestkitchen.com/equipment_reviews/2275-nonstick-rimmed-baking-sheets (`atk_nonstick`)
- verbatim: "The flat cooking surface of a standard rimmed baking sheet measures 16.5 inches by 11.5 inches."
- verbatim: "We don't recommend using cookware with coatings containing PTFE at temperatures above 450 degrees".
- verbatim: "it's ovensafe only up to 425 degrees, while most other nonstick baking sheets are ovensafe to 450 degrees"; another is "the only nonstick sheet we tested that is oven-safe up to 500 degrees".
- verbatim: "Baking sheets marketed as having ceramic nonstick coatings sometimes contain PTFE"; "PTFE-free coatings are especially fragile".
- verbatim: "take care when using metal utensils or placing a wire rack inside these pans, as the nonstick coatings can become scratched."
- Confidence high.

**ATK, Why You Shouldn't Throw Away Your Old Sheet Pan** https://www.americastestkitchen.com/articles/3231-why-you-shouldnt-throw-away-old-baking-sheet-pan (`atk_old_pan`)
- verbatim: "the dull and darkened pans actually browned better than the shiny new ones."
- verbatim: "the older sheets heated faster, hitting just over 400 degrees in 15 minutes. The shiny new sheets only reached 350 degrees in the same amount of time." (single test; numbers kept in notes only)
- verbatim: "oil polymerizes on the surface, like the seasoning of a cast-iron pan".
- Confidence high.

**ATK, The Best Silicone Baking Mats** https://www.americastestkitchen.com/cooksillustrated/articles/627-testing-silicone-baking-mats (`atk_mats`)
- verbatim: "Made of silicone embedded with heat-conducting fiberglass".
- verbatim: "The cooking surface of a standard rimmed baking sheet measures 16½ by 11½ inches, so we preferred mats with close to those same dimensions. Shorter mats reduced the usable surface area; longer mats curved upwards".
- verbatim: "their comparative weight (107 to 117 grams) helps them stay put better than parchment (4 grams)" (single source; notes only).
- verbatim: "Over time, mats accumulate fats and oils and can retain odors"; "Mats that were cleaned in the dishwasher emerged feeling cleaner and less sticky."
- verbatim: "chocolate chip cookies made with melted butter, those baked on the mats were about ¼ inch wider than those cooked on parchment."
- verbatim: Demarle Silpat: "The manufacturer has recently gone out of business. It's still available at some retailers". The Silpat US site failed TLS on every attempt on 2026-10-25, consistent with this; Silpat specs are therefore read from Internet Archive snapshots.
- Confidence high for fit and odour, medium for spread (disputed, below).

**ATK, Is Aluminum Cookware Safe?** https://www.americastestkitchen.com/how_tos/6390-is-aluminum-cookware-safe (`atk_aluminum`)
- verbatim: "Cooking wet, acidic foods in uncoated aluminum is particularly to be avoided"; "imparting a metallic taste and leaving the cookware with a pitted surface"; "Baking cookies on an aluminum baking sheet, in comparison, extracts less aluminum"; "Aluminum cookware that has been anodized ... or clad in a nonreactive material, such as stainless steel or a nonstick coating, does not leach".
- Confidence high (agrees with `atk_rimmed`).

**King Arthur Baking blog, cookie spread test (2022)** https://www.kingarthurbaking.com/blog/2022/12/01/keep-cookies-from-spreading (`kingarthur_spread_blog`)
- verbatim: on the silicone mat "They didn't spread nearly as much as several of the other tests, resulting in cookies that were thick and chewy"; parchment cookies "spread into nice rounds" and "Some of the cookies verged on spreading slightly too much".
- A brand's own test of its own mat, so kind `other`. It contradicts ATK's spread finding; kept as a disagreement.

### Primers and tables

**Wikipedia, Sheet pan** https://en.wikipedia.org/wiki/Sheet_pan (`wiki_sheet_pan`)
- verbatim: "the full-size sheet pan is 26 in × 18 in ... which is too large for most home ovens"; "A half sheet pan is 18 in × 13 in"; table rows Quarter "13 / 9.5", Eighth "9.5 / 6.5", Two thirds "21 / 15".
- verbatim: "Professional sheet pans ... with a 25 mm (1 in) raised lip around the edge".
- verbatim: "a layer of insulation (typically air) designed to protect delicate food from burning (air bake pan)".
- verbatim: "European standard pan dimensions are governed by GN numbers under European Committee for Standardization EN 631."
- verbatim: "quarter sheets will not necessarily nest inside a half sheet side by side".
- verbatim: "Another popular size for home baking is 10 in × 15 in (250 mm × 380 mm). This pan size, traditionally used to make a jelly roll cake, is bigger than a quarter sheet but smaller than a half sheet." Also: "A sheet pan that has a continuous lip around all four sides may be called a jelly roll pan." ATK names half-size pans "Jelly Roll Pan" too (Chicago Metallic, Norpro), so the name is ambiguous.
- verbatim: aluminized steel "combines the conductive, reflective, and food adherence properties of aluminum, with the rigidity, mass, and strength of the inner steel core".
- Confidence high for the size table (matches Vollrath and ATK); the section carries a needs-citations tag, which is why every size is also confirmed against Vollrath.

**Wikipedia, Sheet metal (gauge table)** https://en.wikipedia.org/wiki/Sheet_metal (`wiki_sheet_metal`)
- verbatim: "The larger the gauge number, the thinner the metal." "Gauge differs between ferrous (iron-based) metals and nonferrous metals such as aluminum".
- table, gauge 18: standard steel "0.0478 (1.21)", aluminium "0.0403 (1.02)"; gauge 13 aluminium "0.072 (1.8)"; gauge 16 aluminium "0.0508 (1.29)"; gauge 12 aluminium "0.0808 (2.05)".
- verbatim: ASTM calls gauge "an archaic term of limited usefulness".

**Russ Rowlett, UNC, Sheet Metal Thickness Gauges (Internet Archive, 27 Oct 2013)** (`rowlett_gauges`)
- verbatim table rows: "13 0.0897 0.0934 0.0720"; "16 0.0598 0.0635 0.0508"; "18 0.0478 0.0516 0.0403" (standard steel, galvanized steel, aluminum, inches).
- Confirms the Wikipedia figures. Confidence high.

**Wikipedia, Parchment paper** https://en.wikipedia.org/wiki/Parchment_paper (`wiki_parchment`)
- verbatim: "some brands capable of temperatures up to 420 °F (216 °C)" (not used as a JSON number after review: generic "some brands").
- verbatim: "baking paper is either treated with quilon (a solution of chromium(iii) in an acidic alcohol to modify the cellulose) or coated with silicone."
- verbatim: "Silicone coated parchment paper is not compostable ... Quilon coated parchment paper contains trivalent chromium" (not in JSON).

**Wikipedia, Non-stick surface** https://en.wikipedia.org/wiki/Non-stick_surface (`wiki_nonstick`)
- verbatim: "all manufacturers recommend that temperatures be kept below, typically, 260 °C (500 °F)"; "When pans are overheated beyond approximately 260°C (500°F) the PTFE coating begins to dissociate ... can be lethal to birds."
- verbatim: "Ceramic nonstick pans use a finish of silica ... applied using a sol-gel process without the use of PFAS."

### Brand spec sheets (fields and their order)

**Vollrath Wear-Ever, 5303 / 5303NS / 5301 / 5314 / 5315 / 5220 / 5228** (vollrathfoodservice.com product pages)
- 5303 (half, heavy-duty natural): verbatim table "Overall Dimensions (IN) | 17.8 x 12.9 x 1", "(WB) Width Base (IN) | 16.6", "(DB) Depth Base (IN) | 11.7", "Bead Style | Closed with galvanized wire", "Gauge | 18"; bullet "Galvanized nonrusting rod reinforces closed bead pan".
- 5303NS (half, nonstick): verbatim "consistent baking up to 450°F", "Ideal for baking up to 450°F", "Gauge | 18", "Construction Feature 2 | Standard-duty".
- 5301: verbatim title "16-Gauge Half-size Wear-Ever® heavy-duty..."; "17.8 x 12.9 x 1"; base 16.6 x 11.7; "Gauge | 16".
- 5314: verbatim "17.86 x 12.93 x 1.03", "Gauge | 13", "Bead Style Open", "Open bead pan features heavy-duty 13-gauge construction and does not require a reinforcement rod".
- 5315 (full): verbatim "25.86 x 17.92 x 1.07", "Width Base (IN) | 24.6", "Depth Base (IN) | 16.6", "Gauge | 12".
- 5220 (quarter): verbatim "13 x 9.56 x 1.13", base "12" and "8.6", "Gauge | 16".
- 5228 (eighth): verbatim "9.492 x 6.493 x 1.084", "Gauge | 16", "Bead Style Semi-open". Cited in the JSON as `vollrath_5228` since the blind check, so the eighth size has two sources.
- Field order on the page: model, dimensions (overall, usable, base), size, bead style, finish, duty, material, gauge, induction. Foodservice buyers compare on size, bead and gauge.

**Nordic Ware, Naturals Baker's Half Sheet (Internet Archive, 24 Sep 2026)** (`nordicware_bakers_half`). The live page returned an Incapsula bot wall.
- verbatim: "Outer measurements: 12.9 inches wide, 17.9 inches long. Inner measurements: 12.1 inches wide, 17.1 inches long. Height; 1 inch."
- verbatim: "Encapsulated galvanized steel rims reinforce the entire perimeter"; "whether you are baking at 500 degrees"; "just 1.6 pounds".
- verbatim (missed in the first pass, found by the blind check and re-read 2026-10-25): "Backed by a Lifetime Warranty and oven safe up to 500 degrees Fahrenheit, the Naturals Baker's Half Sheet is built for the long haul."
- verbatim: "Dishwasher use is not advised, as discoloration will occur".
- No gauge is published. The inner figure (17.1 x 12.1) is larger than Vollrath's base (16.6 x 11.7) for the same outer size; we read Nordic Ware's as measured at the rim top, which sloped walls make larger than the floor. ATK measured this pan (model 43100) at "Cooking Surface : 16 1/2 x 11 1/2 in", which confirms the reading.

**USA Pan, Half Sheet Pan, Nonstick (1050HS)** https://www.usapan.com/half-sheet-1050hs (`usapan_half`)
- ATK measured the same model: atk_rimmed "Model Number : 1050HS-UN-1 Material : Aluminized steel Cooking Surface : 16½ x 11½ in Weight : 2.9 lb"; atk_nonstick "Model Number : 1050HS Cooking Surface Size : 16.5 x 11.5 in". So USA Pan's "Baking Surface" is a rim-top figure, like Nordic Ware's "Inner"; the pan is standard size.
- verbatim: "Baking Surface Dimensions: 17.25 x 12.25 x 1 inches"; "Outer Dimensions: 17.75 x 12.75 x 1 inches"; "Material: Aluminized Steel"; "Americoat® Nonstick Silicone Coating"; "Oven Safe Up to 450 °F (230°C)"; "Do not place in dishwasher".

**Silpat mats (Internet Archive snapshots, June and July 2025)** (`silpat_half_mat`)
- Half: verbatim "Dimensions : 11 5/8" x 16 1/2" | 420 x 295 mm"; "Silpat temperatures range from -40°F to 428°F | -40°C to +220°C"; "Composition : Silicone and fiberglass"; "Certifications: All Silpat® products are FDA, NSF and Kosher certified"; "used over 2,000 times".
- Full: verbatim "Dimensions : 16 1/2" x 24 1/2" | 620 x 420 mm" (sits on Vollrath's full-sheet base of 24.6 x 16.6).
- Toaster: verbatim "Dimensions : 7 7/8 inches x 10 7/8 inches | 200 x 275 mm".
- The same page also says "-40°F to 428°F (or -40°C to 240°C)". 428°F is 220°C and 240°C is 464°F, so the page contradicts itself. ATK's mat review lists the same half mat at 500°F: "Model Number : AE420295-07 ... Dimensions : 16.5 × 11.6 in ... Ovensafe to : 500°F". Since the blind check the register treats the Silpat ceiling as disputed (a low-confidence judgement) and uses no Silpat figure in the mat range.
- ATK mats rows, verbatim: Mrs. Anderson's "Model Number : 60000 ... Ovensafe to : 480°F"; model 1041 "Ovensafe to : 450°F" (single source; notes only). Mat range in the JSON is 480 to 500°F: 480 from ATK and the Amazon Basics bullet "Heat resistant up to 480 degrees F"; 500 from ATK (Silpat) and King Arthur.

**King Arthur Baking shop** (`kingarthur_cookie_mat`, `kingarthur_parchment`)
- Cookie mat: verbatim "Fits perfectly into a half‑sheet pan", "Oven‑safe up to 500°F, plus microwave‑ and dishwasher‑safe".
- Half-sheet parchment: verbatim "it nestles perfectly into our half-sheet pans without any curling or adjusting required. It's oven-safe to 450°F"; "Unbleached with no added whitening agents"; "Pre-cut paper fits standard pans".
- Half-sheet parchment, verbatim: "Each sheet of perfectly flat parchment paper measures 16½" x 12¼""; "can be used and reused multiple times before tossing it away". ATK cookie agrees on size: "A standard sheet of parchment (16½ x 12¼ in)". So pre-cut half-sheet parchment is wider than the 11.5 in floor and does not match it.

**Reynolds Kitchens, Parchment Paper with Stay Flat Dispensing** (`reynolds_parchment`)
- verbatim: "oven safe up to 425°F"; "Never touch the parchment paper to an open flame or to the sides of the oven, and do not use with a broiling unit or toaster oven."
- verbatim: "Reinforced Panel Removes Curls so Parchment Stays Flat".

### Regulators, standards and appliance makers

**Minnesota Statutes 116.943** https://www.revisor.mn.gov/statutes/cite/116.943 (`mn_statute_116943`)
- verbatim: "(h) "Cookware" means durable houseware items ... Cookware includes but is not limited to pots, pans, skillets, grills, baking sheets, baking molds, trays, bowls, and cooking utensils."
- verbatim: "(a) Beginning January 1, 2025, a person may not sell, offer for sale, or distribute for sale in this state the following products if the product contains intentionally added PFAS: ... (3) cookware;"
- verbatim: "(q) ... "PFAS" means a class of fluorinated organic chemicals containing at least one fully fluorinated carbon atom."
- verbatim: "(d) Beginning January 1, 2032, a person may not sell ... any product that contains intentionally added PFAS, unless ... currently unavoidable use" (not in JSON).
- The blind check found the live text amended in 2025 and 2026; the quoted subdivisions still read as above.

**Maine Revised Statutes, Title 38, §1614** https://legislature.maine.gov/statutes/38/title38sec1614.html (`maine_statute_1614`), fetched 2026-10-25 (blind-check fix)
- verbatim: "A-10. "Cookware product" means a durable houseware product intended to be used to prepare, dispense or store food ... including, but not limited to, a pot, pan, skillet, grill, baking sheet, baking mold, tray, bowl and cooking utensil."
- verbatim: "effective January 1, 2026, a person may not sell, offer for sale or distribute for sale in this State: ... (2) A cookware product containing intentionally added PFAS".
- verbatim: "F. "Perfluoroalkyl and polyfluoroalkyl substances" or "PFAS" means substances that include any member of the class of fluorinated organic chemicals containing at least one fully fluorinated carbon atom."

**Maine DEP, PFAS in Products** https://www.maine.gov/dep/spills/topics/pfas/PFAS-products/ (`maine_dep_pfas`), fetched 2026-10-25
- verbatim: the prohibitions table lists "January 1, 2026 Cleaning product Cookware product Cosmetic product ..."; "Cookware refers to household products used for the preparation, dispensing, or storage of food and beverages with a surface that contains intentionally added PFAS that comes in contact with food." Second source for the Maine date.
- Other states: not checked. The web-search budget was exhausted, and the one tracker fetched (saferstates.org PFAS page) had no cookware text. The register says "other states were not checked".
- Our reading: PTFE's repeating CF2 unit is a fully fluorinated carbon, so PTFE coatings fall in. Whether reusable PTFE oven liners count as "cookware" under (h) is not settled by the text; not claimed in the JSON.

**Keller and Heckman, Packaging Law, 9 Apr 2024** https://www.packaginglaw.com/news/minnesota-defines-cookware-covered-pfas-ban (`packaginglaw_mn`)
- verbatim: MPCA "considers cookware to mean the specifically listed items in the law, or different forms of the listed items, which include a component that has a nonstick coating containing intentionally added PFAS." Second source for the ban covering baking sheets. The MPCA page itself rendered as 10 words of shell (JavaScript); not read.

**21 CFR 177.2600 and 177.1550, via Cornell LII** (`cfr_177_2600`, `cfr_177_1550`)
- 177.2600 verbatim: "Rubber articles intended for repeated use may be safely used in producing, manufacturing, packing, processing, preparing, treating, packaging, transporting, or holding food"; the elastomer list includes "Silicone (Si) elastomers containing methyl groups."
- 177.1550 verbatim: "Perfluorocarbon resins identified in this section may be safely used as articles or components of articles intended to contact food"; identity includes polymers of "tetrafluoroethylene".
- These are the governing US food-contact rules for silicone mats and PTFE coatings. EUR-Lex (Regulation 1935/2004) returned a 202 shell and was not read; the EU side is a gap.

**National Capital Poison Center, Teflon flu** https://www.poison.org/articles/teflon-flu (`poison_control_teflon`)
- verbatim: "Teflon coating on cookware starts to break down when exposed to temperatures above about 500 °F."
- verbatim: "Case 1. A woman in her 50s was cooking using a Teflon oven liner. Later that evening, she noticed that one of her birds had died suddenly ... Another bird died after she used the Teflon liner again."
- Kind `other`: a poison centre, not a regulator.

**GE Appliances support, Using Aluminum Foil or Silicone Liners** (`ge_foil_liners`)
- verbatim: "Do not use aluminum foil to line oven bottoms. The foil will trap heat below, and disrupt the performance of the oven. The same is true for similar items such as silicone oven liners."
- verbatim: "Gas Ovens: Never cover any slot, holes or passages in the oven bottom ... may cause carbon monoxide poisoning."
- verbatim: "Foil may be used to catch spills by placing a sheet on a lower rack, several inches below the food. Do not use more foil than necessary, and never entirely cover an oven rack with aluminum foil."
- verbatim: "Gas Ovens: Never cover any slot, holes or passages in the oven bottom or cover an entire rack with materials such as aluminum foil. Doing so blocks the air flow through the oven and may cause carbon monoxide poisoning."

**Whirlpool W10795444 Rev B manual (Internet Archive copy; live PDF returned 403)** (`whirlpool_manual`)
- verbatim (pdftotext): "IMPORTANT: To avoid permanent damage to the oven bottom finish, do not line the oven bottom with any type of foil or liner."
- verbatim (pdftotext), next sentence: "For best cooking results, do not cover entire oven rack with foil because air must be able to move freely."
- Whirlpool product help page, verbatim: "Do not line the oven bottom with foil or a liner to avoid permanent damage to the finish."
- Correction 2026-10-25: the first pass attributed "place foil on rack below dish" to this manual. The blind check found no such sentence, and a re-read of the PDF text confirms it is absent. The lower-rack advice rests on GE alone.

### Retail listings (what data is present)

Amazon pages were fetched with curl and the product-information rows read.
- B0049C2S32 Nordic Ware 2-pack: title "Nordic Ware Naturals Half Sheet - USA Made Aluminum Commercial Quality Sheet Pan for Baking or Roasting, Encapsulated Galvanized Steel Rim Prevents Warping, 2-Pack"; rows "Color Natural", "Material Aluminum", "Size 2pk Half Sheet", "Product Dimensions 17.9"L x 12.9"W x 1"H", "Item Weight 1.7 pounds", "Material Type Free Chemical Free", "Unit Count 2 Count".
- B0725GYNG6 Amazon Basics mat: title "... Dishwasher Safe, Food Safe, Heat Resistant, 16.5" x 11.6" ..."; rows "Material Silicone", "Item Weight 0.23 kg", "Item Dimensions L x W 16.5"L x 11.6"W".
- B0DG2RSVK1 Great Jones quarter: "Material Carbon Steel", "Size Little Sheet (13.5" x 9.5")", "Product Dimensions 13.5"L x 9.5"W x 1"H", "Material Type Free PTFE Free"; review variants "Holy Sheet (18.5" x 13.5")".
- B01LZ9YAUO carbon steel set: "Size 17 x 12 x 0.5 inches", "Product Dimensions 17"L x 12"W x 0.5"H", "Item Weight 1.72 kg", "Number of Items 3", an empty "Temperature" row.
- B09QPQVK37 set of 3: title "... 0.8mm Thick Heavy Duty Cookie Tray, Champagne Gold"; "Material Type Free PFOA Free, PTFE Aluminum Lead Cadmium PFOS PFAS Chemical BPA Free"; "Item Weight 4.2 pounds" for three pans.
- Heat ceilings in bullets (found by the blind check, re-read 2026-10-25): Great Jones "Our baking sheet pan is safe up to 450°F"; B01LZ9YAUO "safe for use in ovens up to 420°F (215°C)" plus a brand comparison table with a "Temperature" row (450 / 420 / 550 °F across that brand's products); Amazon Basics mat "Heat resistant up to 480 degrees F". Great Jones title: "Aluminized Steel for Baking, Roasting, Broiling" with "Material Carbon Steel" in the row.
- B09QPQVK37 (HONGBAKE) bullet: "3 nonstick cookie sheets (13''x9'' /15''x10'' /17.5''x12'')", "medium size for baking jelly rolls".
- B0000VYSB6 Regency Wraps, fetched 2026-10-25 (`amazon_regency_liner`): title "Reusable Cookie Sheets, Baking Oven Liner, 17" X 13" PTFE-coated Coated Cookie Sheet Liner"; rows "Material Teflon Coated Sheet", "Sheet Size 17" x 13""; bullets "Cut this baking liner to fit your toaster oven", "hand wash", "safe in temperatures up to 450°F" (single source; number not in JSON). An Amazon search for "ptfe reusable baking liner" returned many such sheets (12 x 16 in "Teflon parchment" sheets, PTFE oven liners), so PTFE pan liners are a real product group.
- What the scraper gets: Material (base metal), Size, Product Dimensions (outer, with height), Item Weight (set totals), Color, Material Type Free (PTFE/PFAS-free claims). Not present as a row on any of the five: gauge, flat floor size, rim construction. Those are marked researched. Heat ceiling is in bullets on coated items (see above), so `max_oven_temp` is now marked listing.

### Could not reach
- Serious Eats sheet-pan and mat reviews (HTTP 402), Wirecutter (403), Food Network (403), KaTom learning centre (403), If You Care parchment (404), MPCA page (JavaScript shell), EUR-Lex (202 shell), Silpat live site (TLS failure), Nordic Ware live site (bot wall).
- The web-search budget for the session ran out partway through; the remaining sources were reached by known URLs, links inside fetched pages, and Internet Archive.
- No enthusiast community was read (Reddit is blocked to fetch tools and search was exhausted). This is a gap: trade-offs rest on ATK and King Arthur testing rather than a community wiki.
- Reusable PTFE pan liners (as distinct from PTFE oven liners) and broiler pans had no dedicated fetched source; the register gives them definitions only, no numbers.

## Data points used for derived metrics

| Item | Outer (in) | Flat floor (in) | Floor area (sq in) | Gauge | Heat ceiling |
|---|---|---|---|---|---|
| ATK standard half | 18 x 13 (listed) | 16.5 x 11.5 | 189.75 | n/a | n/a |
| Vollrath 5303 half | 17.8 x 12.9 | 16.6 x 11.7 | 194.2 | 18 | none stated |
| Vollrath 5301 half | 17.8 x 12.9 | 16.6 x 11.7 | 194.2 | 16 | none stated |
| Vollrath 5314 half | 17.86 x 12.93 | n/a | n/a | 13 | none stated |
| Vollrath 5303NS half | 17.8 x 12.9 | 16.6 x 11.7 | 194.2 | 18 | 450°F |
| USA Pan 1050HS half | 17.75 x 12.75 | 17.25 x 12.25 | 211.3 | n/a | 450°F |
| Nordic Ware Baker's Half | 17.9 x 12.9 | 17.1 x 12.1 (rim top) | n/a | not published | none stated ("baking at 500 degrees") |
| Vollrath 5315 full | 25.86 x 17.92 | 24.6 x 16.6 | 408.4 | 12 | none stated |
| Vollrath 5220 quarter | 13 x 9.56 | 12 x 8.6 | 103.2 | 16 | none stated |
| ATK quarter | n/a | 11.5 x 8.5 | 97.75 | n/a | n/a |
| Silpat half mat | 16.5 x 11.625 | n/a | 191.8 | n/a | 428°F |
| Amazon Basics mat | 16.5 x 11.6 | n/a | 191.4 | n/a | not on listing |
| King Arthur mat | fits half sheet | n/a | n/a | n/a | 500°F |
| Reynolds parchment | roll | n/a | n/a | n/a | 425°F |
| King Arthur parchment | pre-cut half | n/a | n/a | n/a | 450°F |

Gauge to millimetres (aluminum column, both tables agree): 18 = 0.0403 in = 1.02 mm; 16 = 0.0508 in = 1.29 mm; 13 = 0.0720 in = 1.83 mm; 12 = 0.0808 in = 2.05 mm (Wikipedia only for 12). Steel 18 = 0.0478 in = 1.21 mm.

## Numbers in category.json and the sources behind each

| Number | Where | Sources |
|---|---|---|
| Full sheet 26 x 18 in, too big for home ovens | sheet_size, judgement 1 | Wikipedia; Vollrath 5315 (25.86 x 17.92); ATK (won't fit) |
| Half sheet 18 x 13 in | summary, sheet_size, vocabulary | Wikipedia; ATK; Vollrath 5303 (17.8 x 12.9) |
| Quarter 13 x 9.5 in | sheet_size, vocabulary | Wikipedia; Vollrath 5220 (13 x 9.56) |
| Eighth 9.5 x 6.5 in | sheet_size | Wikipedia; Vollrath 5228 (9.492 x 6.493), cited since the blind check |
| Jelly roll 15 x 10 in | sheet_size, vocabulary | Wikipedia (10 x 15); HONGBAKE listing (15 x 10) |
| Half floor 16.5 x 11.5 in | summary, sheet_size, flat_surface_in | ATK rimmed, ATK nonstick, ATK mats; Vollrath 16.6 x 11.7 |
| Half mats 16.5 x 11.6 in | flat_surface_in | Amazon Basics listing; Silpat 16.5 x 11 5/8 |
| USA Pan 17.25 x 12.25, Nordic Ware 17.1 x 12.1 (rim-top figures) | flat_surface_in | the brand pages, each set against ATK's measured 16.5 x 11.5 for the same model |
| Quarter floor about 11.5 x 8.5 | flat_surface_in range | ATK; Vollrath 5220 base 12 x 8.6 |
| About 190 sq in | usable_area_sq_in | arithmetic on the ATK and Vollrath floor |
| 1 inch walls | rim_height, vocabulary | ATK rimmed, ATK cookie, ATK nonstick; Wikipedia 25 mm lip |
| Nonstick 450°F | summary, surface, max_oven_temp, judgement 4 | ATK nonstick; USA Pan; Vollrath 5303NS |
| PTFE breaks down near 500°F | coating_type, vocabulary, judgement 4 | Poison Control; Wikipedia non-stick |
| Parchment 425 to 450°F | max_oven_temp, mechanism family | Reynolds 425; King Arthur 450 (each the maker's own figure) |
| Silicone mats 480 to 500°F | max_oven_temp, liner_material | 480: ATK (Mrs. Anderson's), Amazon Basics bullet; 500: ATK (Silpat), King Arthur. Silpat's own 428 is a disputed judgement only |
| Bare aluminum 500°F | summary, surface, max_oven_temp | Nordic Ware ("oven safe up to 500 degrees Fahrenheit"); ATK nonstick ("You can use them in 500-degree ovens") |
| (range min/max removed) | max_oven_temp.range | a cited listing shows 420°F and a brand table 550°F, so only typical text remains |
| ATK uses uncoated sheets at 500°F | max_oven_temp | ATK nonstick ("You can use them in 500-degree ovens"); Nordic Ware ("baking at 500 degrees") |
| Aluminum half sheet about 1.5 lb | pan_weight | ATK rimmed (1.5); Nordic Ware page (1.6); Amazon (1.7 per pan in a 2-pack row, ambiguous) |
| Stainless more than twice as heavy | surface, mechanism, trade-off | ATK rimmed; ATK cookie (stainless about 4 lb vs 1 to 3 lb range) |
| Gauges 18, 16, 13 in one half size | metal_thickness | Vollrath 5303, 5301, 5314 pages |
| 18 ga aluminum 1.02 mm, steel 1.21 mm; 13 ga 1.83 mm | metal_thickness, thickness_mm | Wikipedia; Rowlett |
| Minnesota 1 January 2025 | coating_type, judgement 5 | statute; Packaging Law |
| Maine 1 January 2026 | coating_type, judgement 5, vocabulary | Maine statute; Maine DEP |

Numbers seen in one source only and kept out of the JSON: ATK's 1 to 2.5 mm favourite thickness, 200 / 165 / 250 sq in cookie-sheet areas, under-2 lb preference, 400 vs 350°F darkened-pan readings, 350°F insulated warp, 107 to 117 g vs 4 g mat and parchment weights, 1/4 inch wider cookies; Silpat's 2,000 uses; ATK's 2 inch big-batch wall.

## Against the existing add-on schema

Add-on read: `supplies/kitchen/add-ons/baking_sheet.jsonc` (sizing.sheet_size_standard enum [full_sheet, half_sheet, quarter_sheet, eighth_sheet, toaster_oven, not_applicable, other, unspecified]; sizing.length; sizing.width), composed with `kitchen-standard.jsonc` (materials with roles; max_heat_temp; dishwasher_safe) and `supplies-standard.jsonc` (high_signal_markdown; sizing: size_stated, pack_count, pieces_included_text, dimensions, capacity, weight, measurements_text). Kinds per AGENTS.md: vertical anchor, quality currency, hard filter, sizing, or high_signal_markdown; photo-answerable facts go to the image pipeline.

| Facet in this register | In the schema today | Proposed kind | Note |
|---|---|---|---|
| product_form | no | hard filter (enum: sheet_pan, reusable_mat, parchment, oven_liner) | The leaf mixes four products with almost no shared spec. Text answers it from the title; the photo usually does too, but parchment versus mat is not reliably visual. |
| sheet_size | yes, `sheet_size_standard` | sizing, hard filter | Keep. Add `two_thirds`. Use the same enum for mats and pre-cut parchment (the pan they fit), and state that in the comment. |
| pan_style | no | image pipeline | Rimmed versus rimless versus broiler pan is what a photo shows; per rule 1 it stays out of the schema. |
| surface | partly: materials (aluminum body, stainless_steel, ptfe_nonstick or ceramic_nonstick coating) | vertical anchor (materials) | Missing value: `aluminized_steel` is not in the materials enum though it is common (USA Pan, ATK's aluminum-coated steel). Proposal: add it, plus `fiberglass` and `paper` for mats and parchment. |
| coating_type | partly: materials coating role ptfe_nonstick vs ceramic_nonstick | hard filter | ATK says some "ceramic" sheets contain PTFE, so the coating name is not the fact buyers filter on. Proposal: `intentionally_added_pfas: enum [yes, no, unspecified]`, a legal-sale fact in Minnesota and a filter buyers type ("PTFE-free"). Amazon's Material Type Free row carries the claim. |
| max_oven_temp | yes, `max_heat_temp` (kitchen-standard) | hard filter | Keep. Comment should say: record null for bare metal with no stated ceiling, not a guessed number. Usually on brand pages, not Amazon rows. |
| broiler_safe | no | derived at query time | From materials and max_heat_temp; not stored (rule 5). |
| flat_surface_in | the add-on's length and width, undefined | sizing, hard filter | The add-on's `length` and `width` duplicate `supplies-standard.sizing.dimensions` unless they are defined as the flat floor. Proposal: keep them only if redefined as cooking-surface length and width (what mats and racks must fit); otherwise cut them as leaf duplicates (rule 5). |
| metal_thickness | no | sizing (it varies by size variant: Vollrath half 18 ga, quarter 16 ga) or high_signal_markdown | Would we happily augment it? Only for the top N, from foodservice spec sheets. That argues for markdown, with `metal_gauge` in sizing only if the team will commit to backfilling it. |
| rim_reinforcement | no | high_signal_markdown | Construction claim; one sentence. |
| insulated | no | high_signal_markdown | Construction; partly visible at the edge in photos. Not a column. |
| surface_color | no | image pipeline | Photo fact. |
| rim_height | standard `sizing.dimensions.height` | sizing (existing) | Already covered; no add-on field needed. |
| pan_weight | standard `sizing.weight` | sizing (existing) | Covered. Comment should say per-pan, not set total. |
| dishwasher_safe | yes (kitchen-standard) | hard filter | Keep. |
| acid_safe | no | derived | From materials; not stored. |
| liner_material | partly: materials (silicone, ptfe_nonstick) | vertical anchor (materials) | Needs `fiberglass` (mat core) as noted above. |
| liner_placement | no | hard filter (enum: oven_floor, rack) | A safety fact: GE and Whirlpool forbid floor liners. Text-only (title or bullets). |
| parchment_format | no | hard filter (enum: precut_sheets, roll) | Text in the title; roll area needs a square-foot unit that `sizing.capacity` lacks (it has cubic_ft, not sq_ft). |

Add-on fields this register considers noise: `sheet_size_standard: not_applicable` (every item in the leaf except oven liners has a size; oven liners can take `other`), the undefined `length`/`width` pair (duplicates of standard dimensions as written), and `supplies-standard.sizing.capacity` for pans (a sheet's capacity is not bought by number). `pieces_included_text` is useful only for sets.

## Branches

Each leg names the register sentence it follows from. Chains of two facts are written out.

**Split 1, product_form ("Pan, reusable mat, parchment, or oven liner?")** The question's four answers are the facet's four values.

- when `sheet pan`: then_ask sheet_size, pan_style, surface; makes_irrelevant liner_material, liner_placement, parchment_format.
  - then_ask: "Pans are judged on metal, thickness and size" (product_form, why experts care); pan_style and surface are defined "For pans".
  - irrelevant: liner_material is defined "For reusable mats and oven liners", liner_placement "For oven liners", parchment_format "Whether parchment comes as ...". None describes a pan.
- when `reusable mat`: then_ask sheet_size, max_oven_temp, liner_material, dishwasher_safe; makes_irrelevant pan_style, surface, coating_type, insulated, rim_height, liner_placement, parchment_format.
  - sheet_size: "A mat must match the pan's flat floor ... or it curls up the walls" (sheet_size).
  - max_oven_temp: "for coated pans, mats and parchment the coating or paper sets it" (definition); "most silicone mats 480 to 500°F" (why; quote updated after the blind check).
  - liner_material: definition "For reusable mats and oven liners".
  - dishwasher_safe: "For silicone mats it runs the other way: ATK found dishwasher-washed mats held less grease and odour" (dishwasher_safe).
  - irrelevant: each pan facet's definition is scoped to the pan ("For pans", "For nonstick pans", "two thin metal layers", "the pan's side wall"); liner_placement and parchment_format as above. The pan annotations metal_thickness, rim_reinforcement and pan_weight are also pan-only but are left off the skip list because they are never asked, only shown, and listing them made the tree unreadable.
- when `parchment`: then_ask parchment_format, sheet_size, max_oven_temp; makes_irrelevant the asked or filtered pan facets (pan_style, surface, coating_type, insulated, rim_height), liner_material, liner_placement. (Changed after the blind check: parchment_format now comes first and dishwasher_safe is no longer marked irrelevant.)
  - parchment_format first: "a roll is trimmed to any pan, so sheet size matters only for pre-cut sheets" (parchment_format why).
  - sheet_size second, for pre-cut sheets: definition covers "the pan a mat or pre-cut parchment sheet is made to fit"; "Pre-cut sheets skip the trimming but fit one pan size" (parchment_format why).
  - max_oven_temp: "Parchment is rated 425 to 450°F by brand".
  - dishwasher_safe leg dropped: its premise was "disposable parchment", but King Arthur says its parchment "can be used and reused multiple times", and no source says parchment cannot be washed. dishwasher_safe is simply not asked on this branch.
  - liner_material irrelevant: defined for "reusable mats and oven liners" only.
- when `oven liner`: then_ask liner_placement, liner_material; makes_irrelevant sheet_size, the asked or filtered pan facets (pan_style, surface, coating_type, insulated, rim_height), parchment_format.
  - liner_placement: "GE and Whirlpool both forbid lining the oven bottom with foil or any liner, and covering an entire rack with foil" (liner_placement). Values now oven floor, full rack, part of a lower rack.
  - liner_material: "a poison-centre case links a PTFE oven liner to a cook's flu-like illness and two dead pet birds" (liner_material).
  - sheet_size irrelevant, chain: sheet_size is defined as the size of a pan or of the pan a mat or parchment fits; the oven liner family is "A sheet that catches drips in the oven itself rather than lining a pan" (mechanism family). So no pan size applies.

**Split 2, sheet_size ("Half sheet, quarter, eighth, or jelly roll?")** No branches: the size answer narrows every product form the same way and changes no later question. Answer mapping: each offered answer is the value of the same name (`jelly roll` added after the blind check); `full` and `two-thirds` are not offered because "they do not fit home ovens" (split rationale); `toaster oven` is no longer offered because "toaster-oven pans have no standard size" (split rationale) and is matched by title words; `nonstandard` is a product value only.

**Split 3, pan_style ("Rimmed for everything, flat cookie sheet, or broiler pan?")** Answers map to the three values in order.

- when `rimmed sheet pan`: then_ask flat_surface_in, rim_height.
  - flat_surface_in: "A rimmed sheet ... takes a wire rack" (pan_style) and "fit depends on the floor" (flat_surface_in). Quote updated after the blind check, since the off-size USA Pan example was removed; the leg stands.
  - rim_height: "ATK wants straight walls at least 1 inch tall on a half sheet" (rim_height).
- when `cookie sheet`: then_ask insulated, surface_color.
  - insulated: "In ATK's cookie test it baked slowly and unevenly" (insulated).
  - surface_color: "a dark nonstick cookie sheet over-browned bottoms" (surface_color) and "rimmed sheets darken from roasting and can overbake cookies" (pan_style). The split rationale now says colour matters on any pan but cookie bottoms show it first; the leg is unchanged.
- No branch for `broiler pan`: no fetched source describes broiler pans beyond ATK's rack-on-sheet alternative, so nothing traceable changes downstream.

**Split 4, surface ("Bare aluminum, stainless steel, or nonstick?")** Answer mapping (split rationale): "bare aluminum" takes bare aluminum and bare aluminized steel, each with its own branch; "stainless" takes stainless steel; "nonstick" takes nonstick coated, ceramic included. Anodized aluminum has no value and is recorded unknown.

- when `nonstick coated`: then_ask coating_type, max_oven_temp; makes_irrelevant acid_safe.
  - coating_type: defined "For nonstick pans".
  - max_oven_temp: "Nonstick ... stops at about 450°F" (surface).
  - acid_safe irrelevant: "Stainless, anodized and coated surfaces do not react" (acid_safe), so the answer is fixed on this branch.
- when `bare aluminum`: then_ask metal_thickness, rim_reinforcement, acid_safe; makes_irrelevant coating_type. (max_oven_temp removed from the irrelevant list after the blind check.)
  - metal_thickness: "it warps readily" (surface) and "Thicker metal heats more evenly and resists warping" (metal_thickness).
  - rim_reinforcement: "Nordic Ware's half sheet and Vollrath's 18-gauge one roll a steel wire into the rim to fight warping" (rim_reinforcement); "Heavy gauge can replace the wire" (same), so the two are read together.
  - acid_safe: "Bare aluminum reacts" (acid_safe).
  - coating_type irrelevant: defined "For nonstick pans".
  - max_oven_temp irrelevant: leg removed. It rested on "Bare aluminum sheets carry no stated ceiling", which Nordic Ware contradicts ("oven safe up to 500 degrees Fahrenheit").
- when `bare aluminized steel` (added after the blind check): then_ask pan_weight; makes_irrelevant coating_type.
  - pan_weight: "Bare aluminized steel bakes alike but is heavier" (surface); ATK weighed the USA Pan bare sheet at 2.9 lb against 1.55 lb for Nordic Ware aluminum (notes only).
  - coating_type irrelevant: defined "For nonstick pans".
  - acid_safe and broiler_safe stay unknown on this branch (no source); they are neither asked nor marked irrelevant.
- when `stainless steel`: then_ask pan_weight, flat_surface_in; makes_irrelevant coating_type, acid_safe.
  - pan_weight: "clad stainless weighs more than twice that" (pan_weight).
  - flat_surface_in: "Most stainless pans are off-size and need their own racks" (flat_surface_in; quote updated after the blind check).
  - acid_safe irrelevant: "Stainless ... do not react" (acid_safe).

Dropped leg: `cookie sheet` makes_irrelevant rim_height. A cookie sheet has raised edges whose height ATK does discuss for grip, so calling wall height irrelevant was weak.

Renderer note: split 2 has no branches and a values list, so the flowchart draws it as a straight step.

## Trimmed detail

Facts cut from capped fields, each kept here:
- summary: ATK's winner is the Nordic Ware Naturals Baker's Half Sheet, which has a wire-stiffened rim; "with a wire-stiffened rim" was cut because ATK does not name the rim as the reason it won.
- surface.why: ATK found stainless "brown food slightly more quickly" (kept in the stainless trade-off).
- sheet_size.why: the two-thirds size is 21 x 15 in (Wikipedia); Silpat's full mat is 24.5 x 16.5 in and its toaster mat 7 7/8 x 10 7/8 in; toaster ovens have no standard pan size in the sources read.
- coating_type.why: Minnesota extends the ban to all products with intentionally added PFAS from 1 January 2032 unless deemed currently unavoidable.
- pan_weight.why: ATK preferred half sheets under 2 lb (single source).
- insulated.why: one insulated sheet warped at 350°F (single source).
- flat_surface_in.why: Nordic Ware's published inner size (17.1 x 12.1) is measured at the rim top.
- liner_material.why: Silpat states FDA, NSF and Kosher certification; Silpat's maker has gone out of business per ATK.
- parchment: King Arthur's is unbleached; Wikipedia says silicone-coated parchment is not compostable and quilon-treated parchment carries trivalent chromium. Not a facet: no buyer-facing source ranks on it.
- metal_thickness: perforated sheet pans exist (Vollrath 5303P; Wikipedia "perforations to aid in speeding cooking (pizza tray)"); left to the `baking-pans` sibling, which owns pizza trays.

## Dropped
- Toaster-oven pan dimensions: no standard in any source; the value stays in sheet_size without numbers.
- Reusable PTFE pan liners as a separate value: no fetched source; PTFE appears only as an oven-liner material.
- A "pinch test" for filler in silicone mats: blog lore, no reliable source.
- Gauge-label inconsistency inside Vollrath's own site (5303 and 5303NS both "Gauge 18" at very different case weights): possibly a data error, notes only.

## Corrections
1. 2026-10-25, before finishing: the parchment ceiling was first written as 420 to 450°F from Wikipedia's "some brands up to 420°F". That is a generic line, not a product rating, so the range now starts at Reynolds' 425°F and `max_oven_temp.range.min` is 425.
2. Single-source ATK numbers (2 inch wall, under 2 lb, 400 vs 350°F, 350°F warp, 1 to 2.5 mm) were removed from JSON prose and kept above.
3. Summary now names America's Test Kitchen in full before using ATK, so the abbreviation is defined at first use.
4. `vertical` is `other`, not `supplies`. The brief asked for `supplies`, but `schema.json` allows only formulations, machines, fashion, furnishing and other, and the validator rejects `supplies` ("'supplies' is not one of [...]"). Sibling registers written in the same run (beverage-chillers, coffee-filters, graters and others) also used `other`. Change it to `supplies` once the schema enum includes it.

## Script problems
- None in the scripts themselves. validate.py, render.py and viewer.py ran clean. The schema's `vertical` enum has no `supplies` value; recorded above.

## Corrections after the blind check (2026-10-25)

Checker report: `check.md` (16 required fixes). Each line is one change; rejected or partial findings say why.

1. Fix 1, bare aluminum ceiling: summary now says Nordic Ware rates its bare sheet to 500°F and ATK broils on it; surface.why, max_oven_temp why, typical and backfill note rewritten; mechanism no longer says bare metal has no ceiling. Sources: Nordic Ware "oven safe up to 500 degrees Fahrenheit"; ATK nonstick "You can use them in 500-degree ovens and put them under the broiler".
2. Fix 1, branch: `max_oven_temp` removed from the `surface = bare aluminum` makes_irrelevant list.
3. Fix 1 and 8, broiler_safe: derivation now true for bare aluminum and stainless (ATK broils on both), false for PTFE nonstick, parchment and mats, maker's claim for PTFE-free nonstick and aluminized steel (Great Jones sells its PTFE-free sheet "for ... Broiling"); backfill note says Nordic Ware's 500°F rating does not mention the broiler.
4. Fix 2, liner placement: liner_placement why now says GE and Whirlpool forbid covering an entire rack with foil and GE's carbon-monoxide warning covers whole racks; values now oven floor, full rack, part of a lower rack; definition and backfill note updated.
5. Fix 2, miscitation: whirlpool_manual supports no longer claims "Place foil on a rack below the dish"; it now cites "do not cover entire oven rack with foil because air must be able to move freely". GE supports gain the whole-rack line. Judgement 7 and the oven-liner family rewritten; the lower-rack advice is credited to GE only.
6. Fix 3, USA Pan floor: removed "USA Pan's floor is 17.25 by 12.25" as an off-size example; flat_surface_in now says brand inner and baking-surface figures are rim-top and that ATK measured both USA Pan 1050HS and Nordic Ware 43100 at 16.5 x 11.5; listing hint limited to Vollrath base and ATK measured rows; backfill_cost raised from medium to high. usapan_half supports reworded.
7. Fix 4, Silpat dispute: new low-confidence judgement (sources disagree) that Silpat's ceiling is disputed, 428°F on its page against 500°F in ATK's mat review; atk_mats now cited on max_oven_temp; mat range in max_oven_temp and liner_material changed from 428 to 500°F to 480 to 500°F (480: ATK, Amazon Basics; 500: ATK, King Arthur).
8. Fix 5, PFAS law: Maine's 1 January 2026 ban added to coating_type why, judgement 5 and the PFAS vocabulary entry, with two new references (Maine statute §1614, Maine DEP). Partial: other states were not checked because the web-search budget was spent; the register now says so instead of implying Minnesota is the only ban.
9. Fix 6, parchment fit: summary now says only mats must match the 16.5 x 11.5 floor; flat_surface_in definition drops parchment. Pre-cut half-sheet parchment is 16.5 x 12.25 (King Arthur; ATK cookie), recorded in references and notes.
10. Fix 7, max_oven_temp range: range min and max removed (a cited listing shows 420°F and a brand comparison table 550°F); only typical text remains. Source changed from researched to listing, with the hint pointing to listing bullets for coated items and brand pages for bare pans.
11. Fix 9, surface mapping: new branch `when: bare aluminized steel` (then_ask pan_weight; makes_irrelevant coating_type); split rationale says aluminized is heavier and that ceramic maps to nonstick; surface backfill note says anodized aluminum is recorded unknown.
12. Fix 10, parchment branch: then_ask reordered to parchment_format, sheet_size, max_oven_temp, and parchment_format why now says a roll fits any pan so size matters only for pre-cut sheets; the dishwasher_safe irrelevant leg dropped (its "disposable" premise is contradicted by King Arthur's "reused multiple times"); product_form definition no longer calls parchment disposable.
13. Fix 10, break-even: mat_break_even_uses formula now divides by uses per parchment sheet, counting one unless the maker allows reuse; evidence now atk_mats and kingarthur_parchment.
14. Fix 11, rim wire: rim_reinforcement why now names Nordic Ware and Vollrath's 18-gauge pan only and says Vollrath's 13-gauge 5314 has an open bead and needs no rod; vollrath_5314 cited and its supports line updated.
15. Fix 12, thickness_mm: formula now takes the base metal from the listing Material row and falls back to a measured mm figure (ATK's Thickness row) for clad stainless or unknown base metal; metal_thickness hint and backfill note mention ATK's mm rows.
16. Fix 13, sheet sizes: `jelly roll` value added (15 x 10 in: Wikipedia, HONGBAKE listing); question now "Half sheet, quarter, eighth, or jelly roll?"; toaster-oven size dropped from the question and matched by title words; backfill note says sets record every size they contain and jelly-roll titles on half-sheet inches are half; vocabulary no longer equates rimmed sheets with jelly roll pans and gains a "Jelly roll pan" entry.
17. Fix 14, PTFE pan liners: reusable mat family and liner_material definition now cover PTFE-coated reusable pan liners; product_form title words add "reusable baking liner" and "cookie sheet liner"; new reference amazon_regency_liner (PTFE-coated, cut to fit).
18. Fix 15, source labels: insulated source changed from researched to derived (title-word match); surface hint says the Material row cannot tell aluminized from carbon steel (Great Jones); vollrath_5228 cited so the eighth size has two sources.
19. Fix 16, pan_style rationale: now says colour matters on any pan but cookie bottoms show over-browning first; the cookie-sheet leg is unchanged.
20. Not changed: the checker's borderline note that sheet_size is not truly novice-answerable was not a required fix; novice_answerable stays true because the definition sits beside the question. coating_type stays source listing at medium cost, which the checker called fair.