# Sleeping bags & camping sleep systems: research notes

Date: 2026-10-25. Scope: the gear a person sleeps in and on while camping or backpacking — sleeping bags (mummy, semi-rectangular, rectangular, double, quilts), sleeping pads/mats (air, self-inflating, closed-cell foam), sleeping bag liners, and camp pillows. This is a bundled taxonomy leaf (`supplies > active > sleeping_bags`, "Sleeping Bags & Camping Sleep Systems"); one register, with `sleep_item_type` as the first split doing the dividing between the four product types rather than four separate registers. Not covered: tents, bivy sacks and hammocks, which sit under the sibling leaf `tents_shelters` (Tents & Shelters) in `catalog.json` even though a bivy sack directly wraps a sleeping bag — left to that sibling because it is a shelter, not sleep insulation. Not covered: cots and camp furniture (sibling `camp_furniture`).

Quote labels: **verbatim** = the sentence in quotation marks was in text I read myself (the fetch tool returned it in quotation marks, or I read it via pdftotext/curl); **fetched excerpt** = the fetch tool summarised or lightly reworded the page in its own words, with quoted fragments inside it coming from the page; **search excerpt** = the claim came from a search-engine summary because the page itself would not load. A search-excerpt-only number does not go in category.json. WebSearch was reported exhausted for this session before I could run a single query (the budget line said "200 of 200" already used by other work in this environment), so every source below was reached by direct WebFetch on a URL I already knew or could guess from brand/standards-body naming conventions. I could not reach Internet Archive snapshots either — WebFetch refused `web.archive.org` outright ("Claude Code is unable to fetch from web.archive.org") — and a direct `curl` from this sandbox to rei.com hung indefinitely (backgrounded, then failed/killed) rather than returning a block page, unlike the 403s WebFetch got from the same domains. So every source here is a live WebFetch; none is an archive snapshot, and REI's own buying guides (normally a strong primer for this category) were unreachable by any method tried.

## Seed

Seed run (recorded verbatim from the brief):

- Example: car-tyres `treadwear_grade`: "a number that is on every listing and still needs a judgement attached, because experts know it only compares within one manufacturer's range."
- Persona: "A pharmacist, who thinks in concentration, delivery form and interactions."

1. **The sleeping-bag equivalent of treadwear is the EN 13537 / ISO 23537 temperature rating.** It is on most mainstream listings, it comes from a standardised lab test, and it still needs a judgement attached for two reasons found in research: (a) not every maker tests to it — GearLab names "Western Mountaineering, Big Agnes, and Feathered Friends" as premium makers who publish their own rating instead (fetched excerpt, switchbacktravel.com); (b) even where it is EN/ISO-tested, the number assumes a specific base layer, hat and insulated pad underneath, so it describes the standard's manikin, not any one sleeper's metabolism. **Kept** as `temperature_rating_f` with a `rating_standard` facet attached (EN/ISO-tested vs the maker's own number), directly mirroring the treadwear pattern. Survived the data check: two independent fetches (switchbacktravel.com, outdoorgearlab.com) and Wikipedia's "Sleeping bag" article all describe the same three-tier comfort/limit/extreme structure.
2. **What the pharmacist notices first: concentration, delivery form and interactions.** "Concentration" maps directly onto fill power — down's insulating value per unit weight, the thing that actually trades off against weight, not raw fill mass. Allied Feather & Down (an industry down processor, fetched excerpt): "the higher the fill power, the greater warmth to weight that material has," and down has "an extremely linear warmth curve," so a pharmacist's instinct to ask for concentration rather than dose is exactly right — fill weight times fill power is closer to the real "dose" than either number alone, which GearLab's own methodology note confirms ("fill weight matters more" than fill power alone, fetched excerpt). "Delivery form" maps onto shape (mummy vs rectangular vs quilt): the same fill delivered as a tapered mummy traps more of its own warmth than delivered as a loose rectangular blanket, for the same ingredient. "Interactions" maps onto down's interaction with moisture: "a soaked down sleeping bag may provide even less insulation than no sleeping bag at all" (Wikipedia, fetched excerpt) — the insulation interacts badly with water the way a drug can interact badly with the wrong co-administered compound, and hydrophobic-down treatment is the industry's answer to that specific interaction. **Kept**: fill_power and fill_weight as a pair rather than either alone, insulation_type as a split with the moisture interaction as its central trade-off, hydrophobic down in vocabulary. **Dropped**: a literal "concentration" derived metric (fill_power × fill_weight) — no source gives this product a name or a verified formula beyond "both matter," so I did not invent one; the register states the relationship in prose and the judgement instead.

## Sources and what each supports

### Standards and the temperature/R-value tests

**Wikipedia, Sleeping bag**
https://en.wikipedia.org/wiki/Sleeping_bag
- fetched excerpt: EN 13537 (2005) "normalizes the temperatures at which a sleeping bag is rated for use," replaced in "October 2016" by "ISO 23537-1:2016." Four ratings: upper limit, comfort (based on a "standard" adult woman), lower limit (thermally neutral), extreme (survival only).
- fetched excerpt: mummy bags taper "from the head end to the foot end, reducing its volume and surface area"; top quilts are "essentially a sleeping bag without a back."
- fetched excerpt: down "retains heat better" but "a soaked down sleeping bag may provide even less insulation than no sleeping bag at all"; synthetic "does not readily absorb water, dries easily, and provides some warmth even when thoroughly soaked" but "cannot be compressed as much and is heavier."
- Supports: the EN/ISO four-tier structure and its 2016 ISO supersession, the quilt definition, the down/synthetic moisture trade-off. Confidence high (encyclopedic secondary source, consistent with the two specialist reviews below).

**Switchback Travel, Sleeping bag temperature ratings**
https://www.switchbacktravel.com/sleeping-bag-temperature-ratings
- fetched excerpt: "still used in many bags" (EN 13537); "ISO testing is so similar to the EN method that we can talk about them as the same." Test uses "a heated manikin wearing long underwear top and bottom, a hat, and a closed-cell foam sleeping pad."
- fetched excerpt: comfort = "the air temperature at which an average female can sleep comfortably through the night"; lower limit = "the air temperature at which a standard male can sleep for eight hours without waking"; extreme = "the temperature at which a standard female can remain for 6 hours without risk of death from hypothermia" (article calls this one undesirable to rely on).
- fetched excerpt: ISO's comfort applies to "cold sleepers," limit to "warm sleepers," replacing EN's gender-fixed wording.
- fetched excerpt: "REI Co-op, The North Face, Marmot, and Mountain Hardwear" use EN/ISO; "Western Mountaineering, Big Agnes, and Feathered Friends do not."
- Supports: the test setup (manikin, base layer, pad), the three practical ratings, the cold/warm-sleeper reframing, and which named brands opt out of the standard. Confidence high; second source for the four/three-tier structure and the opt-out brands.

**OutdoorGearLab, Best backpacking sleeping bag (methodology)**
https://www.outdoorgearlab.com/topics/camping-and-hiking/best-backpacking-sleeping-bag
- fetched excerpt: "Comfort: This rating is recommended for most users... Lower Limit: This is the lowest temperature at which a 'standard man' or warm sleeper can sleep for eight hours... Extreme: This is a rating for survival only." "EN and ISO ratings seem more accurate than manufacturers' previously advertised temperature ratings," though "specific testing protocols may arbitrarily favor certain designs."
- fetched excerpt: lab testing "three nights in each model in a 48°F room"; field testing "nighttime lows between 10°F and 70°F."
- fetched excerpt: down "excellent warmth for its weight, packs smaller... can last for many years with proper care" vs "if a down bag gets wet... it can lose much of its loft"; synthetic "continues to insulate better when damp, dries faster... typically heavier and bulkier."
- fetched excerpt: fill power "typically 500-900"; fill weight is the actual down quantity; "fill weight matters more" than fill power alone for comparing warmth between two bags.
- fetched excerpt: bags "rated 20°F or below" benefit from hood and draft collar; Western Mountaineering UltraLite "high-quality down to maximize warmth"; Exped Terra 15's "thick draft tube fully insulates you from air seeping through the zipper."
- fetched excerpt: zipper quality — "an internal strip of plastic in the adjacent fabric to direct the fabric away from the zipper teeth"; Feathered Friends' "Y-shaped, anti-snag zipper slider."
- fetched excerpt: shell fabrics "12D Extremelite... 10D Pertex Endurance UL" on ultralight bags; REI Trailmade's "DWR coating to effectively shed condensation."
- fetched excerpt: "back sleepers can often take full advantage of traditional mummy bags... side sleepers... often need more space through the shoulders, hips, and knees"; NEMO Disco has "an extra 16 inches of girth compared to ordinary bags." "For maximum warmth, size your bag to fit snugly but not tightly."
- Supports: the three-tier rating as GearLab states it, lab/field test ranges, the down/synthetic trade-off, fill power's typical 500-900 span and the "fill weight matters more" caution, draft collar/tube and zipper detailing, shell fabric denier naming, the mummy-vs-roomy shape trade-off with NEMO's specific girth figure as one product's data point (not generalised). Confidence high.

**Western Mountaineering, UltraLite 20°F sleeping bag (brand spec sheet)**
https://www.westernmountaineering.com/products/ultralite
- fetched excerpt (spec fields as listed): "Temperature Rating: 20°F / -7°C"; "Fill Type & Power: 850+ Power Goose Down"; "Shape: Mummy (w/ full collar)"; "Shell Fabric: 12D ripstop nylon"; total weight by length "5'6": 1 lb 12 oz / 6'0": 1 lb 13 oz / 6'6": 1 lb 15 oz"; fill weight by length "15 oz / 16 oz / 17 oz"; "Loft: 5.5 in (14 cm)"; length options "5'6" (165 cm), 6'0" (180 cm), 6'6" (200 cm)"; inside girth (shoulder/hip/foot) "59"/51"/38"" (5'6" & 6'0") and "60"/52"/38"" (6'6"); stuff size "7"x13""; "Zipper: Full-length #5 YKK, available in Left or Right placement"; lining fabric not stated on the page.
- Supports: what a premium brand's own spec sheet lists and in what order — temperature rating and fill power first, then shape, shell, weight-by-length, fill-weight-by-length, loft, girth, stuff size, zipper side. Confirms fill weight varies by the length variant (see the schema correction below) and that lining fabric is routinely absent even on a thorough spec sheet. Confidence high (one brand's own page; used only for field presence and this one bag's numbers, not generalised ranges).

### R-value and pad construction

**Switchback Travel, Sleeping pad R-value**
https://www.switchbacktravel.com/sleeping-pad-r-value
- fetched excerpt: "R-value measures how well an object resists... heat"; backpacking pad R-values "range from one to seven." The ASTM test standard was "introduced in 2020 by Therm-a-Rest, REI, and MEC through ASTM International," using "a hot plate on top, mimicking the body, and a cold plate below, mimicking the ground," measured "over four hours."
- fetched excerpt: seasonal bands — summer "1 to 3," 3-season "3 to 5," winter/4-season "5+."
- fetched excerpt: "R-values are additive, so you get greater warmth when you stack multiple pads." Example: Exped Dura 8R (R-value 7.8) weighs "2 pounds 1 ounce" vs. Therm-a-Rest NeoAir XLite NXT (R-value 4.5) "1 pound 4 ounces" lighter.
- Supports: the R-value definition, the 2020 ASTM introduction and its three authors, the test method, seasonal bands, additive stacking, and one concrete weight-vs-warmth pair. Confidence high.

**OutdoorGearLab, Best sleeping pad (methodology and buying advice)**
https://www.outdoorgearlab.com/topics/camping-and-hiking/best-sleeping-pad
- fetched excerpt: "Thanks to the new ASTM R-value standardization (astm.org/f3340-18.html), we can now pretty reliably know how well a sleeping pad will insulate if it has a published R-value." Names the standard as "ASTM F3340-18."
- fetched excerpt: seasonal bands — "R-values of 1-2: best for warm nights (warmer than 60°F)"; "3-4.5: insulated enough for '3-season' camping"; ">5: designed for early spring, late fall, or winter camping"; winter specifically wants "at least 6."
- fetched excerpt: inflatable pads are the modern lightweight/warm default; self-inflating pads are "bulkier and heavier than most modern sleeping pads"; closed-cell foam "will not puncture like inflatable pads" and is "quite durable."
- fetched excerpt: stacking — "a closed-cell foam pad... is only warm enough for summer conditions on its own," but placing it under an inflatable "increase[s] the R-value by 2."
- fetched excerpt: "the higher the R-value, the heavier a pad will be."
- fetched excerpt: thickness — "a side sleeper should consider pads that are 3 inches and thicker"; "a back sleeper may be able to comfortably sleep through the night on a 2.5-inch thick pad."
- fetched excerpt: noise — the NeoAir XLite NXT is "considerably quieter than previous versions" but still somewhat noisy; recommends carrying "a mini repair kit" for punctures.
- Supports: second source for the ASTM standard's existence and name (F3340-18), second source for additive stacking and the specific "+2" foam-underneath figure, second source for the general weight-vs-R-value relationship, the three pad construction types, thickness-by-sleep-position, noise and puncture-risk. Confidence high. Note: this source's seasonal bands (1-2 / 3-4.5 / >5, winter 6+) are narrower than Switchback's (1-3 / 3-5 / 5+); both are kept and the register states the disagreement rather than picking numbers that happen to average out.

### Down, fill power and welfare

**Wikipedia, Down feather**
https://en.wikipedia.org/wiki/Down_feather
- fetched excerpt: "down insulation is rated by fill power, which is the number of cubic inches displaced by a given ounce of down"; measured by placing "an ounce of down... into a graduated cylinder" and dropping "a small weight... on top of it."
- fetched excerpt: eiderdown reaches "1200 in³/oz"; "down with a fill power as low as 550 still provides reasonably good insulation"; outdoor gear typically runs "400 to 900 in³/oz"; "500–650 in³/oz... is warm enough and light enough for most conditions"; "800–900 in³/oz fill is used for very lightweight and/or very cold-weather gear."
- fetched excerpt: FTC rules — "100% Down" means only down feathers; "Goose Down" needs "at least 90% goose down, 10% goose feathers."
- Supports: the fill-power test method, the typical range and what "premium" means in it, and the US labeling floor for "goose down." Confidence high.

**Allied Feather & Down, Fill power (industry processor's own explainer)**
https://www.alliedfeather.com/pages/fill-power
- fetched excerpt: "Fill Power is simply a measurement of the volume created by a given amount of down... in most cases, measured in 30 grams per cubic inch." (Elsewhere the standard test is described in ounces; this page states the metric version of the same test.)
- fetched excerpt: "the higher the fill power, the greater warmth to weight that material has"; down has "an extremely linear warmth curve," so in principle half the mass of 1000-fill down matches the warmth of 500-fill down, at better compressibility.
- fetched excerpt: test steps — steam-condition the down (the "US/IDFB steam method"), load 30 g into a standard cylinder, lower a lid, measure volume, average three runs.
- fetched excerpt: "700 fill power" was "historically difficult for duck down to achieve"; "800 fill power duck down" is "now regularly available, rivaling European goose"; "800+ fill power" is "associated with premium material at risk for live plucking."
- Supports: the fill-power test procedure in more detail, the duck-vs-goose achievability gap the add-on schema's own comment already flags, the linear warmth-to-weight relationship, and the live-plucking welfare flag at the top of the range. Confidence medium-high (an industry down processor has an interest in down sounding good, but the test-method description matches Wikipedia's independently, and the welfare caution cuts against the seller's own interest, which raises my confidence in it specifically).

### Liners

**Wikipedia, Sleeping bag liner**
https://en.wikipedia.org/wiki/Sleeping_bag_liner
- fetched excerpt: silk liners are "light, soft and strong and retain much thermal insulation even when wet"; cotton is "heavier and bulkier than silk and absorbs water"; synthetic blends are "usually light, strong, and do not absorb water."
- fetched excerpt: "a thin liner may add 5°F warmth to the bag"; thick fleece-like liners "can increase warmth by 10-15°F."
- fetched excerpt: liners "provide extra comfort, insulation, and help keep the sleeping bag clean," and can be "used alone, without the bag, in hot conditions." A vapor barrier liner (VBL) "blocks the sleeper's moisture from reaching the bag, thus stopping evaporative heat loss." Liners are "issued as basic kit" by the US and British militaries.
- Supports: liner materials and their qualitative trade-offs, the liner-alone and VBL use cases. Confidence high for the qualitative claims. **The specific added-warmth numbers (+5°F, +10-15°F) are single-sourced** — I tried Sea to Summit, REI, Moosejaw, Cocoon and CleverHiker for a second source and every one returned 403/404 — so those two numbers are reported here only, not in category.json, per the two-source rule for numbers.

### Pillows

**OutdoorGearLab, Best camping pillow**
https://www.outdoorgearlab.com/topics/camping-and-hiking/best-camping-pillow
- fetched excerpt: inflatables "use an air bladder... tend to be the lightest, but not necessarily the most comfortable"; compressibles are "a fabric exterior filled with foam or polyester... do not use air for their loft... the most comfortable (but not necessarily the most supportive)"; hybrids have "an air bladder... surrounded by additional batting... heavier than standard inflatable pillows, but offer more support."
- fetched excerpt: Sea to Summit Aeros Down "2.6 ounces," Aeros Ultralight "2.9 ounces," packing to "0.4 liters"; HEST Camp Pillow "51 oz"; Klymit Drift "34.6 oz," scoring "9.9" comfort vs "3.2" packability.
- Supports: the three pillow construction types and the weight/comfort/packability spread across them, with named products as single data points (not generalised). Confidence medium-high (one specialist review; I could not reach a second camping-pillow-specific source, so pillow is kept as the thinnest-sourced of the four item types and its facet is correspondingly modest).

### General primer

**Wikipedia, Camping**
https://en.wikipedia.org/wiki/Camping
- fetched excerpt: "sleeping pad or air mattress to be placed underneath the sleeping bag for cushioning from stones and twigs, as well as for insulation from the ground."
- Supports: the basic reason a pad exists at all (comfort and insulation, not just comfort). Confidence high, background only.

### Could not reach

REI's sleeping-bag and sleeping-pad buying guides (403 on every WebFetch attempt, and a direct `curl` to the same domain hung rather than returning a status code — backgrounded, then failed). Therm-a-Rest's own R-value page (520, then 403). Big Agnes's own R-value explainer page (guessed URL, 404) and a Big Agnes product page (404; the generic brand page loaded but had no spec fields, logged above as a negative result, not used for any claim). Sea to Summit's liner and R-value pages, Cocoon's liner page, Moosejaw's liner guide, CleverHiker's liner guide (all 403/404). Feathered Friends' down-quality and product pages (404 on every guessed URL). Marmot's product page (403). Textile Exchange's Responsible Down Standard page (403) and responsibledown.org (404) — the live-plucking welfare claim therefore rests on the one industry-processor source above, not on the standard's own body. The FTC's textile/down labeling rule page (404; Wikipedia's secondary citation of the same rule was used instead). Reddit's r/Ultralight wiki and Enlightened Equipment's quilt FAQ and GearJunkie's quilt-vs-bag and sleeping-pad pages (Reddit refused outright: "Claude Code is unable to fetch from www.reddit.com"; the rest 403/404) — as a result, quilts are sourced only to the one Wikipedia line above and are kept in the register as a `bag_shape` value with a low-confidence, single-source note rather than given their own split or a quantified weight-savings claim. `web.archive.org` was refused outright by WebFetch for every URL I tried, so no Internet Archive snapshot was used anywhere in this register, unlike some earlier categories' notes.

## Data points used for derived metrics

- `stacked_r_value` (the only derived metric kept): R-values are additive when pads are layered (Switchback Travel, verbatim-quoted "R-values are additive, so you get greater warmth when you stack multiple pads"; OutdoorGearLab, second source, the "+2" foam-underneath figure as one worked example). Formula is literal addition, not invented.
- Considered and dropped: a "down dose" metric (`fill_power × fill_weight`) to formalise the pharmacist's "concentration" framing from the seed. No source names this product or gives a verified conversion to a temperature number, only that both matter and that fill weight matters more in practice (GearLab). Stating a formula I cannot source would be inventing a range, so it stays as prose in `why_experts_care` and the matching judgement, not as a `derived_metrics` entry.
- Considered and dropped: cost-per-degree-of-warmth and cost-per-ounce-saved. Price is excluded from facets by the house rules, and I found no source that computes either number the way Switchback computes additive R-value, so neither is a formula I can defend.

## Against the existing add-on schema

`zamana-expertise/data/schema-parts/supplies/active/add-ons/sleeping_bag.jsonc` already has `temperature_rating` (comfort/limit/extreme/unit), `insulation` (type, fill_power, fill_weight), `r_value`, and `sizing.max_user_height`. It is lean; I do not consider any field in it noise. Proposals only, nothing edited:

| Facet / field | Kind | Call |
|---|---|---|
| `insulation.fill_weight` | currently a plain number under `insulation` | **Correction.** Western Mountaineering's own spec sheet lists fill weight per length variant (15 oz / 16 oz / 17 oz for 5'6" / 6'0" / 6'6"), the same bag's total weight already varies the same way and total weight correctly lives in the generic `sizing.weight`. Per `AGENTS.md` rule 2 ("any field that can differ across size variants... must live INSIDE sizing"), `fill_weight` belongs inside `sizing`, not under `insulation`, which is otherwise variant-invariant (fill type and fill power are fixed per model). |
| `rating_standard` | new enum: `en_iso`, `manufacturer_own`, `unspecified`, sibling to `temperature_rating` | **Addition.** This is the register's direct equivalent of the treadwear judgement: Switchback Travel and GearLab both name specific premium brands (Western Mountaineering, Big Agnes, Feathered Friends) that publish a rating without EN/ISO testing, so the same-looking number means different things depending on this flag. Category quality currency in the sense AGENTS.md means it — the number everyone compares on needs this one qualifier to be comparable at all. |
| `pad_type` | new enum: `air`, `self_inflating`, `closed_cell_foam`, `hybrid` | **Addition.** A hard filter under AGENTS.md rule 4 — stated in the title/description on every pad listing, not reliably read from a photo (an air pad in its stuff sack and a self-inflating pad look alike; a closed-cell foam pad's ridged texture is visible but the other two are not distinguishable by eye), and buyers filter on it directly (durability vs weight vs comfort). The current add-on has `r_value` with nothing that says what kind of pad produced it. |
| `zipper_side` | new enum: `left`, `right`, `center`, `none` | **Addition, lower priority.** A real hard filter (two sleepers matching bags that zip together need opposite sides) stated on every spec sheet I read (Western Mountaineering: "available in Left or Right placement") but narrows the catalog for a minority of buyers, hence `priority.narrows_set` of 2 in the facet below rather than higher. |
| `shape` (mummy / semi-rectangular / rectangular / quilt) | — | **Not proposed as a schema field.** This is visually obvious (a mummy's taper is the single most recognisable silhouette in the category) and AGENTS.md rule 1 puts shape explicitly in the image pipeline's territory. It stays a facet in this register, for the cold-start question and the annotation layer, but the structured value should come from vision embeddings, not a text field. |
| `draft_collar`, `draft_tube`, `hood`, DWR coating | — | **Not proposed as schema fields.** These are exactly the "foldable booleans" AGENTS.md rule 5 calls dead on sight. GearLab tests for them and a buyer cares, but they belong in `high_signal_markdown`, which is already the home for construction and quality signals a line-by-line pass would otherwise need a new boolean for. |
| `loft_in` | — | **Not proposed as a schema field.** Only Western Mountaineering's spec sheet in this research carried it; it is not dense enough across listings to be the "currency we'd happily commit to augmenting" AGENTS.md rule 4 requires. Kept in this register as a researched annotation for top brands only. |
| pad thickness | — | **No new field.** Already covered by the generic `supplies-standard` `sizing.dimensions.height`; the register's `pad_thickness_in` facet below is marked `derived` from that existing field, not a new one, and exists only to carry the sourced "3 in or more for side sleepers" guidance that the raw number alone does not convey. |

## Branches

- `sleep_item_type` = sleeping bag → ask `insulation_type`, `temperature_rating_f`, `rating_standard`, `bag_shape`, `fill_power`, `fill_weight_oz`, `draft_features`, `zipper_side`; makes irrelevant `pad_type`, `pad_r_value`, `pad_thickness_in`, `liner_material`, `pillow_type`. Chain: these are the fields every bag spec sheet and review carries (Western Mountaineering, GearLab); pad- and liner-specific facets have no meaning for a bag. SUPPORTED.
- `sleep_item_type` = sleeping pad → ask `pad_r_value`, `pad_type`, `pad_thickness_in`; makes irrelevant `insulation_type`, `temperature_rating_f`, `rating_standard`, `bag_shape`, `fill_power`, `fill_weight_oz`, `draft_features`, `zipper_side`. Chain: R-value, not a temperature rating, is the pad's warmth number (Switchback, OutdoorGearLab); none of the bag-construction facets apply to a mat. SUPPORTED.
- `sleep_item_type` = liner → ask `liner_material`; makes irrelevant every bag and pad facet above. Chain: a liner's whole job is fabric and how it handles moisture or adds a few degrees (Wikipedia liner article); it has no fill power, no R-value, no shape. SUPPORTED.
- `sleep_item_type` = camp pillow → ask `pillow_type`; makes irrelevant every bag and pad facet above. Chain: pillow construction (inflatable/compressible/hybrid) is its own trade-off (OutdoorGearLab pillow review) unrelated to bag or pad warmth. SUPPORTED.
- `target_season` = winter → then_ask `insulation_type`, `draft_features`. Chain: at R-value 5+/6+ and EN/ISO limit ratings into the cold, draft collars and tubes stop being optional (GearLab: bags "rated 20°F or below" benefit from them) and the down-vs-synthetic wet-performance trade-off matters most exactly when temperatures make condensation and snow contact likely. SUPPORTED.
- `target_season` = summer → makes irrelevant `draft_features`. Chain: draft collars/tubes are named by GearLab as mattering at 20°F and below; a summer-only bag or pad rarely carries them and the feature is not worth asking about. SUPPORTED.
- `trip_style` = backpacking → then_ask `fill_power`, `pad_r_value` (framed against weight); makes irrelevant nothing outright, but the rationale shifts to weight-per-warmth. Chain: GearLab's whole backpacking-bag methodology is built around weighing "the bag, without any included items" and comparing packed size; Switchback's R-value-vs-weight pair (Dura 8R heavier, NeoAir XLite NXT lighter) is the same question for pads. SUPPORTED.
- `trip_style` = car camping → makes irrelevant `fill_power`. Chain: fill power is a weight-efficiency number; GearLab and Switchback only invoke it when comparing packable gear, never when discussing comfort-first car-camping bags, which are usually synthetic-filled rectangular bags bought on warmth and price per the down-vs-synthetic cost comparison (Switchback: synthetic Shasta 15 at "$170" vs down Magma 15 at "$399"). SUPPORTED.
- `insulation_type` = down → then_ask `fill_power`, `fill_weight_oz`; makes irrelevant nothing (synthetic bags still report a fill weight, just not a fill power). Chain: fill power is a down-only measurement (Wikipedia, Allied Feather & Down — the graduated-cylinder test is specific to down clusters). SUPPORTED.
- `insulation_type` = synthetic → makes irrelevant `fill_power`. Chain: same as above, in reverse; synthetic batting has no fill-power number to report. SUPPORTED.

## Trimmed detail

- `rating_standard`: GearLab's own methodology page hedges that "specific testing protocols may arbitrarily favor certain designs" even among EN/ISO-tested bags, so the flag says "tested to a standard" rather than "therefore comparable to the degree."
- `temperature_rating_f`: the ISO wording replaces EN's "standard man"/"standard female" with "warm sleeper"/"cold sleeper," which both sources treat as the same underlying manikin test, not a methodology change — the register's definition uses the newer, ungendered phrasing.
- `pad_r_value`: the two reviewers' seasonal bands differ (Switchback 1-3/3-5/5+; OutdoorGearLab 1-2/3-4.5/>5, winter 6+); the facet's `range.typical` states both rather than averaging them into an unsourced number.
- `fill_power`: Allied Feather's test uses 30 g in a metric cylinder; the FTC/Wikipedia description uses one ounce; both describe the same displaced-volume principle at different sample sizes, not a contradiction.
- `liner_material`: VBLs are liners by construction but work by blocking moisture outward rather than adding insulating loft — kept as a `liner_material` value with that one-sentence distinction rather than a separate facet, since no source gave it enough independent weight to justify one.

## Dropped

- A standalone `quilt` split or a quantified "quilts save N% weight" claim. Real, and widely discussed, but every specific source I tried for it (Reddit's r/Ultralight wiki, Enlightened Equipment's FAQ, GearJunkie, Switchback's and OutdoorGearLab's quilt-specific pages) returned a block or a 404. Only Wikipedia's one-line definition survived, so quilt stays a value of `bag_shape` with a low-confidence note, not its own facet or split.
- Women's-specific sleeping bags as a facet. ISO's move from gendered to "warm/cold sleeper" language (Switchback) already captures the real distinction without needing a sex-specific field, and I found no second source quantifying how much extra insulation women's-cut bags actually add at the core and feet.
- A flammability/safety-standard facet analogous to crib or children's-sleepwear rules. The CPSC's Flammable Fabrics Act page names "children's sleepwear and mattresses and mattress pads" as covered products and does not name sleeping bags; I found no dedicated flammability standard for the category, so none is asserted. The EN 13537 / ISO 23537 temperature rating is this register's governing standard instead, because its real safety stake is hypothermia risk from a mis-rated bag, not fire.
- A `loft_in` split or filter. Real and sourced (Western Mountaineering), but seen on only one of the sources I could reach, so it is a researched annotation, not a split or filter candidate.
- Liner added-warmth numbers (+5°F / +10-15°F) as a JSON fact. Single-sourced (see Liners above); reported here, not in category.json.

## Corrections (2026-10-26)

- Added `vocabulary` entry for "ASTM F3340" linked to `pad_r_value`, matching its sibling bag standard.
- Added `packed_size_l` facet (numeric, L, roles annotation), cited to gearlab_backpacking_bag and gearlab_sleeping_pad SPECIFICATIONS tables (re-fetched live, "Packed Volume" rows confirmed: bags 5.5-9.0 L, pads 0.6-9.0 L), wired into `sleep_item_type`'s bag/pad branches.
- Changed `fill_weight_oz.source` from `listing` to `researched`, matching its own backfill_note.
- Changed `zipper_side.source` from `listing` to `researched`; only evidence is one premium brand's spec page, not ordinary retail listings.
- Added "semi-rectangular" to `bag_shape.cold_start_question` as an explicit option, and added a `vocabulary` entry defining it.
- Dropped `insulation_type` from the `target_season`=winter branch's `then_ask`; it rested on an editorial inference in notes.md (not a quoted source) and duplicated a top-level split already always asked.