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Reference Desk
How a sleeping bag temperature rating is set
Four numbers come out of the test, one goes on the label, and nine in ten listings publish none of them.
Direct answer. A sleeping bag temperature rating is set by a laboratory test using a heated mannequin, standardised in Europe as EN 13537 from 2005 and replaced by ISO 23537-1:2016. The test produces four temperatures — upper limit, comfort, lower limit and extreme — not one. There is no equivalent mandatory standard in the United States, so a 20 °F bag from one maker need not match a 20 °F bag from another. In the catalogue we read on 8 September 2026, only 3 of 290 sleeping-bag listings (1.0%) put any temperature figure in the title, and exactly one cited the standard.
Last verified 8 September 2026 against 290 live US sleeping-bag listings and the published standard, checked during this batch
The four temperatures
Under the standard, a heated mannequin test produces four figures. Manufacturers usually print one of them on the bag.
| Rating | What it means |
|---|---|
| Upper limit | The highest temperature at which a “standard” adult man sleeps comfortably without excess sweating. |
| Comfort | Based on a “standard” adult woman having a comfortable night’s sleep. |
| Lower limit | The lowest temperature at which a “standard” adult man, curled up, is in thermal equilibrium and just not feeling cold. |
| Extreme | A survival-only figure. The standard’s own guidance is that it is not advisable to rely on it for general use. |
The transition zone between the comfort rating and the lower limit is usually treated as the buying guideline. A bag advertised at 0 °C means a person should be able to sleep at 0 °C — not necessarily comfortably.
Why US ratings are not comparable
The standard is European in origin. REI began requiring American manufacturers to follow EN 13537 in March 2010, but there is no mandatory US measurement standard, so two bags labelled 20 °F (−7 °C) from different companies may not deliver the same warmth.
The practical consequence for a buyer is that a rating is comparable within a brand and only loosely comparable across brands unless both cite the standard. In our pull, one listing of 290 did.
What the test assumes about you
The rating is not a property of the bag alone. The test is run on a mannequin wearing long underwear, socks and a hat, sleeping on an insulated pad with an R-value of approximately 5.5.
- Change the pad and you change the rating. A thin foam mat is well below R-5.5, and the ground takes heat faster than the air does.
- Change the clothing and you change the rating. Sleeping in a t-shirt is not the tested condition.
- Moisture reduces insulation. Damp from condensation or sweating measurably degrades a bag’s performance.
- People differ. The comfort and lower-limit figures are explicitly modelled on a standard woman and a standard man, which is a modelling convenience rather than a description of you.
How often the rating is actually published
We checked, because a specification you cannot find is a specification you cannot use. Across 290 US sleeping-bag listings that passed a title screen on 8 September 2026:
| Where the temperature figure appeared | Listings | Share |
|---|---|---|
| In the product title | 3 | 1.0% |
| Anywhere in the retailer’s description | 23 | 7.9% |
| Citing EN 13537 or ISO 23537 by name | 1 | 0.3% |
So more than nine in ten listings for the product whose entire purpose is thermal performance say nothing about thermal performance where a shopper or a script can read it. The three that did put it in the title used the American convention — “40F”, “20F”, “30F” — which is the convention with no standard behind it.
Frequently asked
What does a sleeping bag temperature rating mean?
It is a laboratory figure from a heated-mannequin test defined by ISO 23537-1:2016, which replaced EN 13537 in October 2016. The test yields four temperatures - upper limit, comfort, lower limit and extreme - and a bag usually advertises one of them.
Which of the four numbers should I buy on?
The zone between the comfort rating and the lower limit is generally treated as the buying guideline. The extreme figure is a survival rating and the standard's own guidance is not to rely on it.
Are US temperature ratings comparable between brands?
Not reliably. There is no mandatory US measurement standard, so a 20 degrees F bag from one company may not match a 20 degrees F bag from another. REI began requiring American manufacturers to follow EN 13537 in March 2010.
Does the rating assume anything about my setup?
Yes. The test assumes long underwear, socks, a hat and an insulated pad of roughly R-5.5. A thinner pad, less clothing or damp insulation all reduce real performance.
How many listings publish the rating?
Three of 290 US sleeping-bag listings we read on 8 September 2026 put a temperature in the title, 23 mentioned one anywhere in the description, and one named the standard.
Sources, method and limits
Standard, test structure, the four ratings, the R-5.5 pad assumption, the REI 2010 requirement and the absence of a US standard are from the Wikipedia article on sleeping bags, read 8 September 2026. We have not run the test ourselves and have not used any bag described here.
The publication rates are ours: 5,912 US listings pulled from the CJ product catalogue on 8 September 2026 across twenty outdoor and home-fitness search terms, four pages of 100 rows per term, de-duplicated on advertiser plus title plus destination URL and filtered on each row’s own targetCountry; network demo advertiser rows (77) excluded, leaving 5,835. Asking price is salePrice where present and price otherwise. Sleeping-bag rows were screened on the phrase “sleeping bag” in the title, leaving 290 of 294. A temperature figure was detected as a number followed by a degree symbol or an F or C unit. That pattern will miss unusual phrasings, so read 1.0% and 7.9% as floors.
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How this page was made. Drafted with AI (Claude); not yet independently re-checked. How we work