# Shipping boxes and mailers: research notes

Date: 2026-10-25. Scope: containers a person buys empty to send or move things: corrugated shipping and moving boxes (slotted, die-cut mailer box, multi-depth, long), flexible mailers (poly and paper), padded mailers (bubble and paper-padded), rigid flat mailers and mailing tubes. Out of scope, left to siblings: letter, catalog and document envelopes without padding or stiffening (`cards`, "Envelopes, Cards & Forms"; overlap is the kraft catalog envelope, which stays there), packing tape (`tapes`, under crafts), shipping labels (`labels`), gift boxes and wrap (`gift-bags`; a printed mailer box marketed as a gift box stays here only when sold for shipping). Void fill and bubble-wrap rolls have no leaf in the catalog and are not covered by this register. One register covers both halves of the label; the `format` split does the dividing.

Quote labels: **verbatim** = the sentence in quotation marks was in raw text I read myself (curl plus HTML stripping, or pdftotext on a downloaded PDF); **fetched excerpt** = a fetch tool summarised or reworded the page; **search excerpt** = a search-engine summary. Every quote below is verbatim. No search excerpts were used: the session's web-search budget was exhausted before this run started (every WebSearch call returned "used its web search budget (200 of 200)"), so all sources were reached by fetching known primary URLs directly and following links found inside fetched pages.

## Seed

Seed output, verbatim:

```
=== Example entry (from an unrelated category) ===
category: olive-oil
what this shows: a facet that experts rank first, that almost no listing carries, and that is expensive to backfill. The honest answer is to list it, mark it researched, and limit backfill to the top of the catalog. Also shows a derived metric hanging off a researched facet.

<example>
{
  "id": "harvest_date",
  "label": "Harvest date",
  "definition": "The month and year the olives were picked, as opposed to the best-before date, which is set by the bottler and tells you nothing.",
  "why_experts_care": "Extra virgin oil is a fruit juice and loses the compounds that give it flavour and most of its claimed health effects within about 12 to 18 months of harvest. A bottle with a best-before two years out may already be a year old. People who buy well look for the harvest date and buy within a year of it.",
  "kind": "text",
  "roles": ["annotation", "sort_key"],
  "novice_answerable": false,
  "source": "researched",
  "listing_field_hint": "Rarely present. When it is, it is in a photo of the back label, not a field.",
  "backfill_cost": "high",
  "backfill_note": "Needs a label photo read or a producer page. Backfill the top 100 ranked oils and lazy-load the rest. Where the producer gives only a best-before, record it as unknown rather than guessing.",
  "visual": { "chartable": true, "encoding": "months since harvest on a horizontal scale, with the 12 and 18 month marks drawn" },
  "priority": { "narrows_set": 4, "cost_to_answer": 4 },
  "evidence": ["ucdavis_olive_center", "oliveoiltimes_freshness"]
}
</example>

Derived metric that follows from it:
{
  "id": "months_since_harvest",
  "label": "Months since harvest",
  "formula": "months_between(today, harvest_date)",
  "depends_on": ["harvest_date"],
  "unit": "months",
  "why": "The number a buyer actually needs. Under 12 is fresh. Over 18 and the oil is past the point most tasters would call it extra virgin."
}

=== Persona ===
A tailor, who thinks in fit, drape and what you can alter afterwards

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

1. **The shipping-boxes equivalent of harvest date is the board grade on the box maker's certificate.** It is the strength fact a packaging engineer reads first, it is printed on a bottom flap rather than in a field (Wikipedia: "typically printed on what will become the underside of the box"), and, like best-before versus harvest date, the number printed on it is not the number that matters for parcels. The certificate's gross weight limit (65 lb for 32 ECT or 200# board) is a truck and rail freight limit; IoPP says the certificate "is not a requirement of small parcel carriers and does not indicate that the maximum load shown on the BMC is permissible", and keeps parcel loads to about 30 lb. Uline's chart prints both columns side by side. **Kept**: `board_grade` as a split (via packed weight, which a novice can answer), and judgement 1. **Dropped**: a derived stacking-strength metric using the simplified McKee formula (BCT = 5.876 × ECT × √(perimeter × board thickness), verbatim from Wikipedia's Edge crush test article). Only Wikipedia gives the formula among the pages I could reach, board thickness is not on listings, and Wikipedia itself says "Most estimations do not relate well to other box orientations, box styles, or to filled boxes."
2. **The tailor notices fit first: inside measurements, the allowance for padding, and what can be altered.** Box makers measure the inside, with length and width at the opening and height from the opening to the base (FEFCO), and the existing add-on already flags "outside dims sold as box size" as a trap. The allowance is cushioning room on every side (IoPP: 2 in for fulfillment packing, 3 in for occasional packers). Alteration is the multi-depth box and the variable-depth fold-over mailer, both pre-scored to cut down to the contents (Uline). Drape is the flexible mailer conforming to soft goods, and USPS penalises a lumpy drape: a flat must be "uniformly thick" within 1/4 in or it pays parcel prices. **Kept**: `inside_dimensions` (split), `multi_depth`, `usps_flat_eligible`, `return_strip` (the mailer you can re-close, which is the alteration a recipient makes). **Dropped**: on-demand box-sizing machines (a business purchase, not something sold in this leaf) and the 2 in / 3 in clearance figures from the JSON (one source only; kept here and referred to qualitatively in the register).

## Sources and what each supports

### Standards bodies and trade guidance

**IoPP, Guide to Packaging for Small Parcel Shipments (approved by IoPP Transport Packaging Committee, 3/1/02). PDF fetched live from iopp.org, read with pdftotext.**
https://www.iopp.org/files/public/IoPPSmallParcelShippingGuidelines.pdf
- verbatim: "a box certified as minimum 200 burst or 32 ECT strength has a maximum allowable gross weight limit of 65 pounds for common carrier truck or rail shipments. However, in small parcel shipping the maximum gross weight for average and difficult loads should not exceed about 30 pounds for best performance in product protection. Easy loads may be packed somewhat heavier."
- verbatim: "The BMC is not a requirement of small parcel carriers and does not indicate that the maximum load shown on the BMC is permissible nor that the box will adequately perform in a small parcel system."
- verbatim: "Experience has shown that best results are obtained when contents of the box are limited to about 50% of the maximum gross weight specified on the box manufacturer's certificate (BMC), usually located on a bottom flap."
- verbatim: "Burst grade fiberboard is manufactured to attain certain minimum levels of tensile and tear strength ... ECT grade fiberboard is manufactured to attain a minimum level of crush resistance that relates to good stacking strength ... Although sufficient stacking strength is an important attribute needed in small parcel systems, durability is even more important ... Durability is closely related to tensile and tear properties."
- verbatim (Type 2, fulfillment): "a minimum of two (2) inches thickness of protective or space between contents and container walls should be provided." (Type 3, occasional): "At least three (3) inches of cushioning material of sufficient strength for item weight should be used on all six sides of the item."
- verbatim: "Bags, bundles and wraps should not be used with difficult loads." "For easy and average loads up to 20 pounds, reinforced paper bags and padded bags with at least 60-pound basis weight paper exteriors are acceptable. For easy loads up to five (5) pounds, plastic bags should be at least 2-mil thick polyethylene or equivalent. For easy loads up to 10 pounds, bags should be at least 4-mil thick."
- verbatim: "Difficult loads are items that require a high degree of protection to prevent puncture or distortion ... Fragile objects and delicate instruments (having a fragility of 50 G's or less), high density items, and small bulk items are in this category."
- verbatim: "The regular slotted container (RSC) style of box works well with most items and packing operations. For heavy loads over 50 pounds, a full overlap style (FOL) will prevent breakouts better than the RSC style." "any style box having non-uniform surfaces or faces should be avoided if at all possible".
- verbatim: "Corrugated fiberboard is approximately one-half as strong in stacking strength at 85% relative humidity (RH) as in normal testing conditions of 50% RH." "Boxes in storage for a long period (approximately one year) retain about one-half of their original compression strength."
- verbatim (tubes): "sidewalls should have equivalent strength of solid fiberboard 1/8 inch thick for tubes under 18 inches long, 5/32 inch thick for tubes 18 to 32 inches long, 3/16 inch thick for tubes over 32 to 60 inches long, and ¼ inch thick for tubes over 60 inches long."
- verbatim: "Other types of containers such as bags, tubes or wood boxes are sorted on auxiliary systems such as carts, pallets, or slower moving conveyors."
- Supports: certificate versus parcel weight, ECT versus burst, bag and padded-bag limits, film floors, box styles, humidity, tube walls, clearance. Confidence high; dated 2002 but the physics and the USPS rules below still match it.

**FEFCO, International Fibreboard Case Code, 12th edition (2022). PDF fetched from fefco.org, pdftotext.**
https://www.fefco.org/sites/default/files/files/FEFCO%20Code_WEB%287%29.pdf
- verbatim: "All dimensions are expressed as internal dimensions in mm as follows: Length (L) x Width (W) x Height (H). Length (L): Longer dimension at the opening. Width (W): Shorter dimension at the opening. Height (H): Dimension from the top of the opening to the base".
- verbatim: "Slotted boxes consist of basically one piece with a glued, stitched or taped manufacturers joint and top and bottom flaps." (0200 series; 0201 is the first style). "Folder boxes and trays are usually made from one piece of board. The bottom of the box is hinged to form two or all side walls and the cover." (0400 series, which includes 0427). The FEFCO landing page adds "a new series related to retail and e-commerce".
- Supports: the inside-dimension convention and the slotted-versus-folder style split. Confidence high.

**How2Recycle (GreenBlue), label pages and FAQ (curl).**
https://how2recycle.info/about-the-how2recycle-label/store-drop-off-us-only/
- verbatim: "In the US, plastic bags, wraps, and films aren't accepted in most curbside or drop-off programs. However, many of these packages are eligible for Store Drop-off recycling." The qualifying list includes "plastic mailers with compatible label".
https://how2recycle.info/frequently-asked-questions/
- verbatim: "In the US, only pure polyethylene (PE) films are recyclable through the Store Drop-off stream. Plastic mailers can only be recycled in the Store Drop-off stream if the paper label has been fully removed."
https://how2recycle.info/about-the-how2recycle-label/widely-recyclable/
- verbatim: "Packages with this label are accepted by 60% of America's recycling facilities and 50% of Canada's."
- Supports: plastic mailers are not curbside; label removal; the 60 percent line. Confidence high.

### Regulators

**USPS Domestic Mail Manual 601, Mailability (curl).** https://pe.usps.com/text/dmm300/601.htm
- verbatim 4.5: "Plastic bags must be polyethylene or equivalent and at least: For loads up to 5 pounds: 2 millimeters thick. For loads up to 10 pounds: 4 millimeters thick." (The unit reads millimetres; IoPP's identical rule reads mil. See judgement 3.)
- verbatim 4.4: "For loads of up to 20 pounds, reinforced bags or bags with a minimum of 70-pound basis weight are acceptable. Nonreinforced loose-fill padded bags are not acceptable as exterior containers, unless the exterior ply is at least 60-pound basis weight."
- verbatim 4.2: "Solid and corrugated fiberboard boxes may be used for loads up to 70 pounds or according to the limits in 3.0. ... The size of the box must be adequate to contain the items and provide enough space for cushioning material."
- verbatim 3.9 (soft goods): "From 20 up to 45 pounds: At least 200-pound test board. From 45 to 70 pounds: At least 275-pound test board." 3.10 (sound recordings): "From 40 to 65 pounds ... 200-pound test fiberboard containers ... More than 65 pounds: Shipments weighing more than 65 pounds must be packaged in 275-pound test fiberboard containers or equivalent."
- verbatim 4.3 (tubes): "The length must not exceed 10 times the girth." Sidewall "At least 1/16 inch thick for tubes less than 18 inches long. At least 3/32 inch thick for tubes 18 to 32 inches long. At least 5/32 inch thick for tubes more than 32 inches long."
- verbatim 3.13: "Loose-fill cushioning must overfill the container before closure to hold the item and prevent its movement within the container."
- Supports: film floors, padded-bag exterior, 275-pound board for heavy parcels, tube rules. Confidence high.

**USPS DMM 101, Physical Standards (curl).** https://pe.usps.com/text/dmm300/101.htm
- verbatim 2.1: flat-size mail is "Not more than 15 inches long, or more than 12 inches high, or more than 3/4 inch thick. Flexible (see 2.3). Rectangular ... Uniformly thick (see 2.4)."
- verbatim 2.3: "Boxes—with or without hinges, gaps, or breaks that allow the piece to bend—are not flats."
- verbatim 2.4: "any bumps, protrusions, or other irregularities do not cause more than 1/4-inch variance in thickness."
- verbatim 6.4: a Ground Advantage retail parcel includes "A flat-size mailpiece, regardless of thickness, that is rigid or nonrectangular."
- verbatim 6.1: "First-Class Mail (letters and flats} must not exceed 13 ounces." 3.2.2: "no mailpiece may weigh more than 70 pounds."
- Confidence high.

**USPS DMM 201, Commercial Letters, Flats and Parcels (curl).** https://pe.usps.com/text/dmm300/201.htm
- verbatim: "Be not more than 15 inches long or more than 12 inches high or more than 3/4 inch thick"; 8.3.1: a parcel is "A flat-size mailpiece, regardless of thickness, that is rigid or nonrectangular."
- Supports: second statement of the flat limits (commercial side of the same manual). Confidence high.

**USPS DMM 123 and 133, dimensional weight (curl).** https://pe.usps.com/text/dmm300/133.htm and https://pe.usps.com/text/dmm300/123.htm
- verbatim 133.1.4.1: "Postage for USPS Ground Advantage parcels ... exceeding 1 cubic foot (1,728 cubic inches) is based on the actual weight or the dimensional weight ... whichever is greater."
- verbatim 133.1.4.2: "Measure the length, width, and height in inches. Round up ... each measurement to the nearest whole inch. Multiply the length by the width and then that total by the height. [7-12-26] If the result exceeds 1,728 cubic inches, divide the result by 139 and round up ... to the next whole number". 123.1.3.2 (Priority Mail) says the same.
- Note: the "[7-12-26]" tag marks a 12 July 2026 revision. Wikipedia still gives the older USPS factor of 194 for Priority Mail; the manual is current and wins.
- Confidence high.

**USPS, Sending Letters (usps.com, curl).** https://www.usps.com/ship/letters.htm
- verbatim: "If your large envelope is nonrectangular, rigid (can't bend), or lumpy (not uniformly thick), you'll have to pay the package price." "For large envelopes up to 13 oz, the price varies for each additional 1 oz."
- Supports: second source for rigid and lumpy mailers paying package prices and for the 13 oz flat ceiling. Confidence high.

**USPS, Sending Packages (usps.com, curl).** https://www.usps.com/ship/packages.htm
- verbatim: "If you're using your own packaging, dimensional (DIM) weight may apply, so always enter your package's dimensions in the USPS Price Calculator". "Use strong packaging with enough room to add cushioning for fragile items and to prevent items from shifting."
- Supports: DIM weight on your own box; room for cushioning. Confidence high.

**USPS Notice 123, Price List (curl; effective October 04, 2026).** https://pe.usps.com/text/dmm300/Notice123.htm
- verbatim: "Parcels that exceed 22 inches but not greater than 30 inches in length, add $4.50. Parcels that exceed 30 inches in length, add $21.00. Parcels that exceed 2 cubic feet (3456 cubic inches), add $35.00. Parcels that contain any of the following characteristics, add $4.50: a. Cylindrical tubes or rolls".
- Used in notes only (single source); not cited in the JSON.

**FTC Green Guides, 16 CFR 260.12 (Cornell LII, curl).** https://www.law.cornell.edu/cfr/text/16/260.12
- verbatim: "When recycling facilities are available to a substantial majority of consumers or communities where the item is sold, marketers can make unqualified recyclable claims. The term "substantial majority," as used in this context, means at least 60 percent."
- Supports: the 60 percent line behind an unqualified "recyclable" claim. Confidence high.

### Spec sheets

**Uline, 12 x 6 x 6" Long Corrugated Boxes S-4128 (curl).** https://www.uline.com/Product/Detail/S-4128/Corrugated-Boxes-200-Test/12-x-12-x-12-Corrugated-Boxes (the URL slug says 12 x 12 x 12; the page served is the S-4128 long box)
- verbatim table header: "MODEL NO. INSIDE DIMENSIONS L x W x H"; "DIMENSIONS: Outside: 12 3/8 x 6 3/8 x 6 5/8" (+/- 1/8")"; "All FedEx and all UPS Dimensional Weight: 4 lbs"; "MATERIAL: C flute"; "All boxes open along the length (first dimension)."
- verbatim: "200# Test vs 32 ECT (Edge Crush Test): 200# Test: 60% stronger bursting strength. Recommended by UPS for shipping up to 40 lbs. 32 ECT: Recommended by UPS for shipping up to 30 lbs. ... 200# test boxes withstand 200 lbs/sq.in. of side wall pressure before bursting. ... 32 ECT boxes withstand 32 lbs/linear inch of stacking weight before crushing."
- verbatim: "BOX STRENGTH GUIDELINES: (Maximum weight per box) FIBRE BOX HANDBOOK UPS GUIDELINES 32 ECT Single Wall 65 lbs 30 lbs 200# Single Wall 65 lbs 40 lbs 275# Single Wall 95 lbs 65 lbs 350# Single Wall 120 lbs 80 lbs 200# Double Wall 80 lbs 60 lbs 275# Double Wall 100 lbs 80 lbs 350# Double Wall 120 lbs 100 lbs 500# Double Wall 160 lbs 140 lbs".
- Confidence high for what Uline prints; the UPS column is Uline's restatement of UPS guidance, which I could not read directly (ups.com returned Access Denied).

**Uline, Multi-Depth Boxes (curl).** https://www.uline.com/BL_407/Multi-Depth-Boxes
- verbatim: "MULTIPLE SIZES IN 1 BOX – CUT DOWN TO THE SIZE YOU NEED Minimize UPS and FedEx dimensional weight pricing by eliminating empty box space. Sides are creased at intervals - Just cut to the creased height needed". Example row: "S-4706 8 x 8 x 8" 8,7,6,5,4"".

**Uline, Kraft Easy-Fold Mailers (curl).** https://www.uline.com/BL_1301/Kraft-Easy-Fold-Mailers
- verbatim: "ADJUSTABLE DEPTH Protect and ship multiple catalogs, books and other printed materials. Adjustable - Scored at variable depths. 200 lb. test, B-flute."

**Uline, Moving Kits (curl).** https://www.uline.com/BL_7907/Moving-Kits
- verbatim: "S-4163 Small 16 x 12 x 12" 200# ... S-4456 Medium 18 x 18 x 16" 200# ... S-4338 Large 18 x 18 x 24" 200# ... S-4676 Dish Boxes 18 x 18 x 28" 350# DW ... S-4750 Wardrobe Boxes 24 x 20 x 46" 51 ECT DW".
- Single source for moving-box sizes (U-Haul timed out; Home Depot returned 403 to curl and WebFetch). Used only for the family line "dish and wardrobe boxes are double wall".

**EcoEnclose, Padded Envelopes; Poly Mailers; Rigid Mailers; Paper Mailers (curl).**
https://www.ecoenclose.com/shop/padded-envelopes/ — verbatim: "EcoTec Mailers Expanded adhesive sandwiched between kraft paper provides light protection"; "Paper Bubble Mailers Embossed paper mimics air bubbles ... Curbside recyclable with paper."; "Padded Mailers Upcycled newspaper sandwiched between recycled Kraft paper. Ideal for shipping fragile items."; "Bubble Mailers Thin-film recyclable, tear strip for easy opening, and a second adhesive strip for reuse."
https://www.ecoenclose.com/shop/shipping-packaging/poly-mailers/ — verbatim: "Recycled Poly Mailers Thin-film recyclable, tear strip for easy opening, and a second adhesive strip for reuse."
https://www.ecoenclose.com/shop/shipping-packaging/rigid-mailers/ — verbatim: "When bending isn't an option, rigid mailers step in. They keep prints, photos, and flat goods crisp"; "Thick 28pt paperboard"; "Extra-thick 36 pt paperboard ensures products do not bend."
https://www.ecoenclose.com/shop/shipping-packaging/paper-mailers/ — verbatim: "Apparel Mailers ... Ideal for shipping soft goods."; "Kraft Mailers Lightweight paperboard ... Ideal for shipping lightweight soft goods."

**UPS, Shipping dimensions and weight (Internet Archive snapshot 2025-10-27, curl on 2026-10-25 after the blind check).** https://web.archive.org/web/20251027072758/https://www.ups.com/us/en/support/shipping-support/shipping-dimensions-weight.page
- verbatim: "Dimensional Weight = (L x W x H) ÷ Divisor". "For each measurement, start at the longest point, rounding each measurement to the nearest whole number." "Increase any fraction to the next whole pound. Note: The divisor varies by rate type: 139 for Daily Rates; 166 for Retail Rates."
- Supports: UPS 139 (daily) and 166 (retail); UPS rounds sides to the nearest inch, USPS rounds up. Wikipedia's UPS entry says the same (139 daily rates above 1 cu ft; 166 "Retail rates only, for all packages"). Confidence high for the archived date; ups.com itself still refuses curl.

**FedEx, How to Pack (2012 PDF, Internet Archive snapshot 2015-11-23, pdftotext).** https://web.archive.org/web/20151123220911/http://www.fedex.com/us/services/pdf/How_To_Pack.pdf
- verbatim: "Wrap product(s) individually with at least 2" thickness of air-cellular cushioning or foam material to fit snugly inside a corrugated box." Diagram label: "Packing material (e.g., loosefill peanuts) minimum of 2" thickness on each side".
- verbatim (dimensional weight, 2012): "divide by 166 (for U.S. and Puerto Rico shipments) or 139 (for international shipments)". This disagrees with Wikipedia's later 139 for FedEx US, so no FedEx divisor goes in the JSON.
- Supports: second source for IoPP's 2 in clearance. Dated (2012); confidence medium.

### Specialist and primer sources

**EcoEnclose, Designing for Recyclability (curl).** https://www.ecoenclose.com/resources/designing-for-recyclability
- verbatim: "An all-poly bubble mailer can be recycled; a poly bubble interior/paper exterior cushioned mailer cannot."
- verbatim: "cushioned paper whose interior substances are unknown to the sorter (i.e., paper mailers cushioned with poly-bubble or expanded foam), and materials that can be mistaken for plastic can cause issues at the MRF and be sorted out accidentally."
- verbatim: "Plastic film (LDPE or HDPE) can be recycled but must be put in a special thin film bin, meaning that they are source separated."
- verbatim: "~88% of US residents have ready access to a recycling program that accepts corrugated boxes." (single source; notes only)
- Confidence medium: a packaging seller, but the page is a technical primer and agrees with How2Recycle where they overlap.

**EcoEnclose, Suffocation warnings (curl).** https://www.ecoenclose.com/blog/suffocation-warnings-legal-packaging-requirements/
- verbatim: "Various state and city regulations require flexible film packaging that is 1 mil or less thick to carry suffocation warnings. On the other hand, Amazon FBA requires sellers to use poly bags that are at least 1.5 mil thick".
- Checked for the safety rule. These laws target thin product bags; mailers meeting the 2 mil parcel floor sit above the 1 mil line. Single source, so it is not in the JSON; recorded here so the child-safety question was examined, not skipped.

**Wikipedia, Corrugated fiberboard (raw wikitext).** https://en.wikipedia.org/wiki/Corrugated_fiberboard
- verbatim: "The letter designation relates to the order that the flutes were invented, not the relative sizes." "The most common flute size in corrugated boxes is "C" flute." "Finer flutes such as E and F flutes provide smoother printing surfaces for high-resolution graphics, making them widely adopted for custom retail packaging and mailer boxes." "Boxes are usually specified and ordered by the internal dimensions." The box maker's certificate is "typically printed on what will become the underside of the box" and lists "Bursting Test or Edge Crush Test", "Size Limit", "Gross Weight Limit". Flute table (from the Wiley Encyclopedia of Packaging Technology): A 3/16 in, B 1/8 in, C 5/32 in, E 1/16 in, F 1/32 in (single source; notes only).

**Wikipedia, Corrugated box design (raw).** https://en.wikipedia.org/wiki/Corrugated_box_design
- verbatim: "The most common box style is the Regular Slotted Container (RSC)." "an RSC is coded 0201." "If long-term storage of corrugated boxes in high humidity is expected, extra strength and moisture resistance is called for."

**Wikipedia, Edge crush test (raw).** https://en.wikipedia.org/wiki/Edge_crush_test
- verbatim: "It gives information on the ability of a particular board construction to resist crushing." Simplified McKee formula "BCT = 5.876 × ECT × √(U × d)" (dropped; see Seed).

**Wikipedia, Dimensional weight (raw).** https://en.wikipedia.org/wiki/Dimensional_weight
- verbatim: "The shipping fee is based upon the dimensional weight or the actual weight, whichever is greater." FedEx "U.S. and Puerto Rico: 139 cuin/lb"; UPS "U.S. Domestic: 139 cuin/lb ... (Daily rates only, for packages that exceed one cubic foot ...)". "The freight carrier will measure the longest dimension in each of the three axes".
- Dated: the UPS and FedEx citations are 2016 to 2017 archive links, and ups.com and fedex.com both refused curl and WebFetch on 2026-10-25 (Access Denied; FedEx "System Down"). Uline's current "All FedEx and all UPS Dimensional Weight: 4 lbs" on a 432 cubic inch box fits 139 (432 ÷ 139 = 3.1, rounds up to 4) and not 166 (2.6, rounds to 3). So 139 for UPS and FedEx stands on Wikipedia plus that Uline data point; medium confidence.

**Wikipedia, Padded envelope (raw).** https://en.wikipedia.org/wiki/Padded_envelope
- verbatim: "The padding is usually thick paper, bubble wrap, or foam." "The exterior envelope can be made of a heavy paper, paperboard, corrugated fiberboard or plastic film." Life-cycle study: "overall, the Kraft padded mailer had a higher overall environmental impact compared to the LDPE bubble mailer" (Pilfold 2013, University of Calgary MSc thesis; the thesis itself not read).

### Could not reach
- ups.com and fedex.com (packaging guidelines, dimensional weight pages, PDFs): Access Denied or System Down to curl and WebFetch, live and via the Internet Archive (archive.org timed out). After the blind check, archive.org answered: the UPS dimensional-weight page (snapshot 2025-10-27) and FedEx's 2012 How to Pack PDF were read; FedEx's current dimensional-weight pages were still unreachable.
- U-Haul and Home Depot moving-box pages (timeout, 403).
- Pirate Ship support (403 challenge page).
- Reddit seller communities: not attempted after the search budget was gone; the community slot is weak in this register. The trade's own guidance (IoPP, FEFCO, How2Recycle) carries the expertise instead.

## Data points used for derived metrics

| Item | Inside L × W × H (in) | in³ | ÷139 | billed DIM (rounded up) | ÷166 | cu ft |
|---|---|---|---|---|---|---|
| Uline S-4128 long box | 12 × 6 × 6 | 432 | 3.11 | 4 (Uline states 4) | 2.60 → 3 | 0.25 |
| Uline S-4128, outside rounded up | 13 × 7 × 7 | 637 | 4.58 | 5 | | 0.37 |
| Uline small moving | 16 × 12 × 12 | 2,304 | 16.6 | 17 | | 1.33 |
| Uline medium moving | 18 × 18 × 16 | 5,184 | 37.3 | 38 | | 3.00 |
| Uline large moving | 18 × 18 × 24 | 7,776 | 55.9 | 56 | | 4.50 |

Uline's 4 lb figure matches inside dimensions; carriers measure the outside (USPS: "Measure the length, width, and height in inches. Round up"; Wikipedia: the carrier measures the longest dimension on each axis). So the billable-weight metric uses outside dimensions, and a listing's inside dimensions understate it, here by one pound.

Box strength, UPS guideline as a share of the certificate (Uline table): 32 ECT 30/65 = 46%; 200# SW 40/65 = 62%; 275# SW 65/95 = 68%; 350# SW 80/120 = 67%; 200# DW 60/80 = 75%; 275# DW 80/100 = 80%; 350# DW 100/120 = 83%; 500# DW 140/160 = 88%. IoPP's "about 50%" matches single wall at the light end; double wall is allowed closer to its certificate.

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

| Number | Where in JSON | Sources |
|---|---|---|
| 32 ECT / 200# certificate limit 65 lb | board_grade, judgement 1 | IoPP (verbatim), Uline Fibre Box Handbook column (verbatim) |
| about 30 lb parcel limit for 32 ECT | board_grade, split 3 | IoPP (verbatim, average and difficult loads), Uline UPS column 32 ECT 30 lb (verbatim) |
| 200# single wall: about 30 lb (IoPP) versus 40 lb (Uline UPS column) | board_grade, split 3, judgement 2 | the two sources disagree; recorded as a disagreement, 200# kept with a warning above 30 lb |
| 200-pound board for soft goods 20 to 45 lb | usps_dmm_601 reference, judgement 2 | USPS DMM 601 3.9 (verbatim); context only, not used as a threshold |
| 275-pound board for the heaviest parcels | board_grade | USPS DMM 601 3.9 and 3.10 (verbatim), Uline UPS column (275# SW 65 lb, double wall 60 to 140 lb) |
| 2 mil to 5 lb, 4 mil to 10 lb | film_thickness_mil, judgement 3 | IoPP (verbatim), USPS DMM 601 4.5 (verbatim, unit misprinted) |
| padded bags to 20 lb | padding_type | IoPP (verbatim, padded bags, easy and average loads); USPS DMM 601 4.4 gives 20 lb for reinforced or 70-pound bags only, so the USPS half is indirect and the JSON says so |
| flat: 15 × 12 × 3/4 in, flexible, uniformly thick | usps_flat_eligible | USPS DMM 101 2.1 and DMM 201 (verbatim) |
| rigid or lumpy mailer pays package price | usps_flat_eligible, format | USPS DMM 101 6.4, usps.com letters page (verbatim) |
| 13 oz flat ceiling | usps_flat_eligible | USPS DMM 101 6.1, usps.com letters page (verbatim) |
| 139 cubic inches per pound (USPS above 1 cu ft; UPS daily rates) | mechanism, billable_weight, judgement 9 | USPS DMM 133 and 123 (verbatim); UPS page, archive 2025-10-27 (verbatim); Wikipedia UPS entry; Uline DIM 4 lb data point |
| 166 cubic inches per pound (UPS retail rates) | mechanism, billable_weight, judgement 9 | UPS page, archive 2025-10-27 (verbatim); Wikipedia UPS entry (verbatim) |
| 0.785 nonrectangular factor; 70 lb dimensional-weight cap | billable_weight | USPS DMM 133 1.4.2 and 1.4.3, DMM 123 1.3.2 and 1.3.3 (verbatim, two sections of the manual, as for 139) |
| at least 2 in of cushioning on every side | inside_dimensions, split 2, cushion_room_in | IoPP Type 2 (verbatim), FedEx How to Pack 2012 (verbatim) |
| 1 cubic foot (1,728 in³) USPS DIM threshold | billable_weight, cubic_feet | USPS DMM 133, Notice 123 (verbatim) |
| 60 percent for an unqualified recyclable claim | judgement 7 | FTC 16 CFR 260.12 (verbatim: consumers or communities). How2Recycle's Widely Recyclable 60% counts recycling facilities, a different base; the JSON now says so and cites that page (`how2recycle_widely`) |

Numbers kept out of the JSON because only one source carries them: IoPP's 3 in clearance for occasional packers (the 2 in figure went back in after the blind check, with FedEx as second source), FedEx's dimensional-weight divisor (Wikipedia 139 from 2017 citations versus FedEx's own 2012 guide at 166), 50 percent of the certificate, half strength at 85% RH, FOL above 50 lb; Uline's UPS weights other than the 30 lb line; moving-box sizes; Notice 123 length and tube surcharges; flute thicknesses; EcoEnclose's 28 pt and 36 pt rigid board and the 1 mil suffocation line; the 88 percent corrugated access figure.

## Against the existing add-on schema

Add-on read: `supplies/stationery/add-ons/shipping_box.jsonc` (`wall_type`, `sizing.inside_dimensions_raw`, `sizing.max_weight`), composed with `stationery-standard` (empty) and `supplies-standard` (`high_signal_markdown`, `sizing.size_stated`, `pack_count`, `pieces_included_text`, `dimensions`, `capacity`, `weight`, `measurements_text`). Kinds follow AGENTS.md rule 4: vertical anchor, quality currency, hard filter, sizing.

| Facet in this register | In add-on today | Proposed kind | Note |
|---|---|---|---|
| format | no | hard filter (enum: flexible_mailer, padded_mailer, rigid_mailer, mailing_tube, corrugated_box) | The leaf bundles boxes and mailers; without this field every other field is ambiguous. Text-derived from the title. |
| inside_dimensions | yes, `sizing.inside_dimensions_raw` (string) | sizing, numeric | Proposal: replace the raw string with `sizing.inside.{length,width,height,unit}` plus `dimensions_basis: enum [inside, outside, unstated]`. Buyers filter by number, and DIM weight needs numbers. Keep the add-on's trap comment. |
| board_grade | partly, `wall_type` | quality currency | Proposal: `board_test: {method: enum [ect, burst], value: number}` beside `wall_type`. "32 ECT" and "200#" are on different scales, so one number field without the method is wrong half the time. |
| (box weight limit) | yes, `sizing.max_weight` | drop, or keep with a basis enum | Ambiguous between the certificate limit (65 lb for 32 ECT) and the parcel guideline (about 30 lb). If kept, add `max_weight_basis: enum [box_certificate, carrier_guideline, seller_claim]`; otherwise derive from board_test at query time. It is variant-invariant for a given board, so it need not sit in `sizing` unless the seller states it per size. |
| mailer_material | no | hard filter (enum: paper, polyethylene, paper_with_plastic_lining) | Decides curbside versus store drop-off. Text fact. |
| film_thickness_mil | no | quality currency (poly mailers only) | The one number poly mailers are compared on, and USPS and IoPP set floors on it. Would augment from brand pages. |
| padding_type | no | high_signal_markdown | Partly visible in photos (bubble versus paper); the recyclability consequence is carried by mailer_material. |
| usps_flat_eligible | no | derived at query time | From format, inside dimensions and thickness; not stored. |
| box_style | no | out of schema (photo) | AGENTS.md rule 1: a lid-style mailer box versus a flapped RSC is answered by the photo. The register keeps it as an annotation for the assistant. |
| flute | no | high_signal_markdown | Brand spec tables carry it ("C flute", "B-flute"); worth a line, not a column. |
| multi_depth | no | high_signal_markdown | A feature claim; rule 5 cuts curated feature vocabularies. Titles say "multi-depth". |
| return_strip | no | high_signal_markdown | Same reasoning. |

Add-on and standard fields this register considers noise for this leaf: `sizing.capacity` (a box's volume follows from its dimensions; rule 5 cuts fields derivable from kept fields), `sizing.weight` (the empty container's own weight changes nothing a buyer decides, except as a tiny part of postage), `pieces_included_text` (a bundle of identical boxes is `pack_count`), `measurements_text` (superseded by `high_signal_markdown` per rule 3). `pack_count` stays: boxes and mailers are sold in bundles of 25 to 500 and per-unit cost depends on it. `wall_type`'s `not_applicable` value is right for mailers.

## Branches

Trace as of the blind-check fixes (2026-10-25). Legs that point only at facets nobody can be asked about (novice_answerable false, no question) were removed; those facets stay as card annotations and filters.

Split 1, `format` ("Clothes, small sturdy things, flat or rolled prints, or fragile or heavy?"). Answers map to values by the rule in `format.why_experts_care`: clothes → flexible mailer; small sturdy things → padded mailer (IoPP: bags are for easy loads, "not readily damaged by puncture or shock"); flat prints → rigid flat mailer; rolled prints → mailing tube; fragile or heavy → corrugated box.

- when `corrugated box`: then_ask board_grade, multi_depth; makes_irrelevant mailer_material, film_thickness_mil, padding_type, usps_flat_eligible, return_strip.
  - board_grade: its definition is "the certified strength of the corrugated board", and it is a split with a question.
  - multi_depth: definition is about the box; it has a question ("Many different item sizes from one stock of boxes?").
  - box_style removed from then_ask (blind check): novice_answerable false, no question. It stays an annotation on box cards.
  - usps_flat_eligible irrelevant: DMM 101 2.3 verbatim "Boxes ... are not flats".
  - mailer_material, padding_type, film_thickness_mil, return_strip irrelevant: each definition names a mailer.
- when `flexible mailer`: then_ask mailer_material, return_strip; makes_irrelevant board_grade, box_style, flute, multi_depth, padding_type.
  - film_thickness_mil removed from then_ask (blind check): no question; it stays an annotation and filter on poly mailer cards, and the mailer_material `paper` branch still drops it.
  - return_strip: EcoEnclose lists it on poly mailers ("Recycled Poly Mailers ... a second adhesive strip for reuse").
  - padding_type irrelevant: the family line defines a flexible mailer as "an unpadded envelope".
  - board_grade, box_style, flute, multi_depth irrelevant: corrugated-only by definition (multi_depth's only mailer case, fold-over book mailers, is binned as corrugated box).
- when `padded mailer`: then_ask mailer_material, return_strip; makes_irrelevant board_grade, box_style, flute, multi_depth.
  - padding_type and usps_flat_eligible removed from then_ask (blind check): neither has a question; usps_flat_eligible is derived and depends on contents thickness.
  - return_strip added (blind check): EcoEnclose verbatim "Bubble Mailers Thin-film recyclable, tear strip for easy opening, and a second adhesive strip for reuse."
- when `rigid flat mailer`: makes_irrelevant usps_flat_eligible, film_thickness_mil, padding_type, board_grade, flute, mailer_material, box_style.
  - usps_flat_eligible: fixed at no. DMM 101 6.4 "A flat-size mailpiece, regardless of thickness, that is rigid" is a parcel; usps.com "rigid (can't bend) ... you'll have to pay the package price".
  - board_grade, flute, box_style: the family line says stiff paperboard, not graded corrugated (EcoEnclose "Thick 28pt paperboard"); box_style is defined for corrugated boxes.
  - mailer_material added (blind check): a rigid mailer is always paperboard (EcoEnclose "28pt paperboard", "36 pt paperboard"), so the value is fixed and the question has nothing to choose.
- when `mailing tube`: makes_irrelevant usps_flat_eligible, mailer_material, padding_type, film_thickness_mil, board_grade, flute, box_style, multi_depth, return_strip.
  - usps_flat_eligible: nonrectangular pieces are parcels (DMM 101 6.4).
  - box_style, multi_depth, return_strip added (blind check): box_style is defined as how a corrugated box is cut and folded; multi_depth is pre-creasing of a box or mailer; return_strip is "on a mailer". A fiberboard tube with end caps (family line; DMM 601 4.3 "fiberboard tubes") is none of these.
  - the rest: defined for mailers or corrugated board.

Split 2, `inside_dimensions` ("Item's length, width and height, before padding?"): no branches. Mapping now stated in `inside_dimensions.why_experts_care`: for a box, each item dimension plus 4 in (2 in of cushioning on each side: IoPP Type 2 "a minimum of two (2) inches thickness of protective or space between contents and container walls"; FedEx How to Pack, 2012, "minimum of 2" thickness on each side") is the minimum inside size. For mailers the register filters on width and length and leaves the fit allowance to the buyer, because no source gives one.

Split 3, `board_grade` ("Packed box under 30 lb, or heavier?"): no branches. Answers map by the rule in `board_grade.why_experts_care`: under 30 lb → "single wall, 32 ECT", "single wall, 200#", "single wall, stronger than 200# or 32 ECT" or "double wall"; 30 lb or more → removes "single wall, below 32 ECT or 200#" and "single wall, 32 ECT", keeps "single wall, 200#" with a warning (IoPP about 30 lb for average and difficult loads; Uline's UPS column 40 lb; judgement 2), and keeps the stronger grades. "not stated" stays in both, unfiltered. A heavy-load leg to box_style (IoPP: FOL above 50 lb) stays dropped: box_style has no question and the 50 lb line is single-source.

Split 4, `mailer_material` ("Paper mailer for the recycling bin, plastic, or either?"): "paper for the bin" → `paper`; "plastic" → `plastic (polyethylene)`; "either" → no filter (all three values stay), stated in `mailer_material.why_experts_care`.

- when `paper`: makes_irrelevant film_thickness_mil. Film thickness is defined for "a plastic mailer's film".
- The `plastic (polyethylene)` branch (then_ask film_thickness_mil) was removed after the blind check: its only target has no question. The plastic answer now sets the filter value; film thickness shows on the cards.
- No branch for `paper outside, plastic bubble inside`: nothing downstream changes beyond the split's own filter.

## Trimmed detail

Sentences cut from capped JSON fields that carried a fact; each is kept elsewhere or lives only here.

- summary: "IoPP's parcel guide, FEFCO and USPS agree on all three points" (attribution; kept in the references).
- mechanism: the flute letters and their order (kept in `flute` and vocabulary); "USPS applies dimensional weight only above 1 cubic foot" (kept in the billable_weight metric).
- board_grade.why_experts_care: Uline's full UPS-guideline ladder (200# 40 lb, 275# SW 65 lb, 350# SW 80 lb, 200# DW 60 lb, 275# DW 80 lb, 350# DW 100 lb, 500# DW 140 lb). Single source; table above.
- inside_dimensions.why_experts_care: the Uline outside-dimension example (12 3/8 × 6 3/8 × 6 5/8 in for a 12 × 6 × 6 in box) and IoPP's 2 in / 3 in clearance. Single source each; above.
- format.why_experts_care: IoPP's definition of difficult loads (fragile at 50 G or less, high density, small bulk items).
- usps_flat_eligible.why_experts_care: the 1/4 in uniform-thickness tolerance (DMM 101 2.4; one section of one source).
- box_style.why_experts_care: IoPP's FOL "over 50 pounds" threshold.

## Corrections

- 2026-10-25, before publishing: the Priority Mail DIM factor of 194 in Wikipedia was replaced by the manual's current 139 (DMM 123, revised 7-12-26). The first draft of the board-grade split had three weight bands (under 30, 30 to 65, over 65); the 65 lb break for parcels rests on Uline's UPS column alone, so the split was cut to two answers at the 30 lb line, which has two sources.
- 2026-10-25, STYLE.md pass on the JSON prose: removed unsourced catalog shares from two split rationales ("which is most parcels", "roughly in two"); replaced invented padded-mailer examples (books, cables, cosmetics) with the sourced condition (items that will not break); dropped "triangular" tubes and "round" certificate stamps (not in any source); removed Uline's 40 lb figure for 200# board from the ECT-versus-burst trade-off (single source); defined "flat" at its first use in the mechanism; trimmed summary (64 to 58 words), mechanism (151 to 149) and one reference line to the caps.
- Viewer: the skill's `tests/viewer-browser.py` was run on a temporary copy (1380, 768 and 390 px, light and dark, offline): 6 of 6 PASS. The flowchart is wider than the panel at 1380 px and scrolls horizontally, as designed.

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

Findings from `check.md` (11 required fixes). Sources re-fetched by curl into the scratchpad `fix-shipping-boxes/`: UPS dimensional-weight page (archive 2025-10-27), USPS DMM 123, 133 and 601, IoPP PDF, Uline S-4128, How2Recycle Widely Recyclable, Wikipedia Dimensional weight (raw), FedEx How to Pack (archive). FedEx's live pages still refused.

1. board_grade: values now separate "single wall, below 32 ECT or 200#", "single wall, 32 ECT", "single wall, 200#", "single wall, stronger than 200# or 32 ECT" and "double wall"; scale-neutral names instead of naming ECT equivalents for 275#, since no fetched source gives an equivalence.
2. board_grade and split 3: the heavier answer removes 32 ECT and lighter single wall and keeps 200# with a warning, instead of removing 200#; IoPP's "average and difficult loads" qualifier added; unsourced "Under 30 lb any rated single-wall box works" removed from the rationale.
3. New judgement 2 (sources_disagree true): 200# single wall about 30 lb (IoPP) versus 40 lb (Uline's UPS column); notes that USPS allows 200# for soft goods to 45 lb.
4. Judgement 1 note: added "average and difficult loads".
5. Dimensional weight: mechanism now gives 139 at USPS and UPS daily rates, 166 at UPS retail; judgement 9 (was 8) restated the same way with the UPS archive page as evidence; FedEx dropped from the claim, because its only 139 source is Wikipedia's 2017 citations and FedEx's own 2012 guide says 166.
6. billable_weight: formula adds the 0.785 nonrectangular factor and the 70 lb cap (DMM 133 and 123), the UPS versus USPS rounding rule and both divisors; depends_on now names outside_dimensions, packed_weight_lb, format and dimensions_basis; evidence adds `ups_dim_weight`.
7. New references `ups_dim_weight` (UPS page, archive) and `fedex_how_to_pack`; `wiki_dimweight` supports line corrected to UPS 139 daily, 166 retail.
8. Branches: removed then_ask legs to facets with no question (box_style on corrugated box; film_thickness_mil on flexible mailer; padding_type and usps_flat_eligible on padded mailer; film_thickness_mil on the plastic branch, which was removed with it).
9. mailer_material: question now "Paper mailer for the recycling bin, plastic, or either?" so the plastic answer sets `plastic (polyethylene)`; mapping updated; skip_if_known adds rigid flat mailer.
10. inside_dimensions: the cushioning allowance is now stated (at least 2 in per side; IoPP plus FedEx 2012), with the box mapping item + 4 in per dimension; mailers sized by width × length, fit allowance left to the buyer; split 2 rationale updated; `cushion_room_in` gets the 2 in threshold.
11. inside_dimensions source changed to listing (backfill low), and the inside-versus-outside basis split into a new researched facet `dimensions_basis` (inside, outside, not stated; backfill medium).
12. film_thickness_mil: IoPP's floors now said to be for easy loads; the facet no longer says USPS sets a mil floor (USPS prints millimetres, our reading stays in judgement 4); backfill raised to medium with a top-N note.
13. format: question now offers "flat or rolled prints", and rolled prints map to mailing tube; IoPP's easy-load definition added to why_experts_care and as a vocabulary entry.
14. Scope boundaries in the JSON (format backfill_note): unpadded catalog envelopes to `cards`, storage boxes to `storage-containers`, gift boxes to `gift-bags`. Judgement 10 (storage) reworded to boxes kept stacked after a move, with the storage-containers boundary in its note.
15. padding_type, multi_depth, return_strip: source changed to derived; multi_depth "absent means no" changed to unknown; padding_type no longer relies on the photo.
16. box_style: the RSC default flagged as our heuristic in backfill_note, and photo checks marked as research for the top N.
17. Missing legs added: padded mailer then_ask return_strip; rigid flat mailer makes mailer_material and box_style irrelevant; mailing tube makes box_style, multi_depth and return_strip irrelevant.
18. How2Recycle split into three references (Store Drop-off page, FAQ, Widely Recyclable page), so each claim cites the page that carries it; judgement 7 (was 6) now says the FTC counts consumers or communities and How2Recycle counts facilities.
19. padding_type and the `usps_dmm_601` reference: the USPS 20 lb figure is now stated as applying to reinforced or 70-pound bags, not padded bags.
20. Vocabulary: FEFCO code no longer "used worldwide"; now "the European box industry's numbering".
21. Summary: rolled prints in a tube added; last sentence shortened to stay under 60 words. Mechanism trimmed in two places to fit the divisor clause under 150 words.
22. seed.dropped: the 2 in clearance line updated, since it is back in the JSON.

Not done, with reasons:
- Fix 6, tube wall facet: not added. Listings rarely state the wall, and IoPP and USPS give different minimums at every length (judgement 6), so a facet would have no threshold either source agrees on. It stays a judgement.
- Fix 4, the 3 in clearance for occasional packers: still left out. Only IoPP gives it in that context (FedEx's 3 in is for computers in a box-in-box), so it stays in notes.
- Fix 1, a 40 lb answer: the question keeps two answers at 30 lb. A third answer at 40 lb would rest on Uline's UPS column alone.
- `vertical`: still "supplies", as the authoring brief requires. validate.py still reports the one schema error noted below, so `.ready` was not written.

## Script and schema problems

- `schema.json` restricts `vertical` to formulations, machines, fashion, furnishing, other. The brief requires `"vertical": "supplies"`, which the catalog also uses. `validate.py` therefore reports exactly one schema error on this register (`vertical: 'supplies' is not one of [...]`). A copy with `vertical` set to `other` validates clean, which shows nothing else is wrong. Scripts and schema were not modified. render.py and viewer.py were run directly after validation, since the documented `&&` chain stops at the validator.