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EN13537 Sleeping Bag Temperature Ratings Explained

Bloody Mary Sleeping Bag

US outdoor manufacturers and retailers have adopted a new sleeping bag temperature rating standard called EN13537 that was originally developed in Europe. While it helps consumers compare different sleeping bags, it can be a bit difficult to understand.

EN13537 Explained

There are three ratings that you need to pay attention to when evaluating a sleeping bag rated using EN13537: Comfort, Lower Limit, and Extreme.

  1. The comfort rating is for women (I don’t know why they didn’t just label it women.) Women need more insulation when they sleep than men.
  2. The lower limit is for men and designates the lowest temperature at which a man can remain comfortable in the sleeping bag, provided he’s wearing long johns and sleeping on a 1″ pad.
  3. The extreme limit designates the coldest temperature you could survive without freezing to death. I find this an odd thing to put on a consumer tag, but it is what it is. Beware of this rating. Online retailers sometimes quote it as the lower limit or the comfort rating of the bag (#2) because they don’t understand what information to print.

Accurate Product Listings

REI is one of the leading proponents of the EN13537 temperature rating standard in the states, and their sleeping bag product descriptions demonstrate their commitment to clearly articulating the recommended temperatures for women and men. For example, if you check out the Specs tab of any sleeping bag sold at REI, you’ll see the following lines listed.

  • EN lower limit (rating for men) ## degrees Fahrenheit
  • EN comfort (rating for women ## degrees Fahrenheit

Consumer Protection

The EN13537 sleeping bag temperature standards provides consumers with the ability to make relative comparisons of the insulating value of different sleeping bags. That’s a good thing and sleeping bag temperature ratings have become much more realistic.

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  1. I agree with you that all three values [comfort, lower, extreme] should be shown and that using the extreme value is seriously, and potentially dangerously, misleading.

    The Valandre web site lists the extreme temperature as the bag's rating; making the same "error" as the US site. The Valandre web site does link to the test report so that helps; but still a curious way to state the bag’s performance.

    I had a few cold nights early on due to believing the sleeping bag manufacturer's ratings for temperature. I educated myself and I will never buy a sleeping bag without an EN13537 rating again.

    I don't have the same concerns as you do with regards to the EN13537 sleeping bag temperature rating standard. The standard provides a uniform and consistent procedure. The values obtained by applying the standard may not be accurate but they are precise and that is the most you can expect for a standard of this nature [so many variables, including what is comfortable?].

    By that I mean, once you have a standard rating that can be used to compare various bags you can then apply your "personal rating adjustment". So the ratings may not be accurate for each person but the ratings give a value that can be used to approximate how the various bags will perform for you.

    For example, I learned through experience that the EN13537 lower limit rating is a conservative rating for me. Another person may need to add or subtract from that number but EN13537 lower limit rating serves a standard reference.

    I would be concerned with the EN13537 standard if two independent testing companies applied the standard to the same bag and certified ratings that were different by the standards published margin of error (showing my old QA/QC background there…). No one seems to be making that argument.

    Bottom line – once you have purchased a sleeping bag, you need to learn, through trail and error, what additional layers you need to sleep comfortably at various ambient temperatures. That is a process that everyone must go through. I suggest you make your errors when you are close to the trailhead.

    • IMHO, a uniform and quantitative testing standard for sleeping bag thermal performance is invaluable to the consumer (obviously keeping the 3 test ratings straight). Of course all details of the test must be performed to a uniform standard (probably more carefully done in European laboratories). It must be combined with your own calibration experiment using a tested bag for a far more effective system to make good decisions on bag purchase and use. Confusing the issue by finding faults with the details are not that useful. Being careful to compare apples to apples gets you information far better than nothing.

      Its the only way you can tell if a bag will keep you warm enough before you spend alot of money and go out and freeze in the wilderness because manufacturers could rate bags anyway they wanted. I won’t buy a bag without this rating.

      My calibration experiment is a North Face SnowShoe 0 degree synthetic bag at its limits around 25 degrees F for me with all my clothes on, down booties with a NeoAir mattress and a bivy sack.
      I need to research if this bag is EN 13735 rated as I’ve had for >10 years, hopefully I am not out of luck! I’ve emailed North Face about this also. No more borderline chilly nights in the mountains for me!


  2. I kind of like these ratings. While not perfect, they give a better temp rating for those who are "warm" sleepers and "cold" sleepers. Maybe they should call it this instead of Male/Female.

    Regardless, this will help clear up some of the subjectivity of previous temps ratings. I've seen countless online forums debate how people felt in a particular temp-rated bag; some would be comfortable beyond the rating, while others wouldn't even come close.

    The T-Extreme is an odd thing too. There are many factors that go into determining when one freezes to death: water and wind being some of them.

    Finally, I have bought some LaFuma bags in the past, and know that they have been using this rating system as well. However, they're a Euro manufacturer, not a US retailer.

  3. trail and error….hahahahaha

  4. Tom – you said

    "I would be concerned with the EN13537 standard if two independent testing companies applied the standard to the same bag and certified ratings that were different by the standards published margin of error (showing my old QA/QC background there…). No one seems to be making that argument."

    On the contrary, people have noted that inter-test center reliability is poor because the way in which people interpret the test conditions varies: see this post for more info:

    If you're a manufacturers and don't like a center's test results, shop around and find a center that gives the bag a lower test score…

  5. I use the Big Angus sleeping bags. I have the down overbag +40 degrees and a down +15 degree….It will be interesting what that makes it rate-trial & error could be a tough night testing the extremes

  6. Tom – to clarify. I'm not against EN13537. I think it's a good thing if the test can be documented well enough so that tests in china match those in the US and Europe. Lord known we need something to standardize sleeping bag ratings. After that we need to re-educate the retailers and consumers to understand the ratings and document them in understandable and accurate ways.

  7. Hi Phil,

    If you could shop around for the best rating, then the standard would definitely need to be reworked. I don't believe anyone is proven that is the case.

    We had the same disagreement in the previous post back in Sept.

    Dr. McCullough's main criticism was that there MAY be some inter-lab variability but Dr. McCullough did not state any evidence to support this opinion. Dr. McCullough was, overall, very supportive of the standard.

    The other report referenced in the Sept Post states:

    “The results imply that the test accuracy achieved is + 1.8° C on the T Comfort, and + 2.6° C on T Extreme. Put simply, these results suggest that the test is only half as accurate as it is specified. In other words, the “error bars” should be twice as big as stated.”

    So their criticism was that the EN standard produced an accuracy of “ONLY” 1.8 deg C and not to the specified 1.0 deg C accuracy that the EN standard states that it can achieve.

    So +/- 5 deg F margin of error rather than +/- 3.2 deg F margin of error. To me, they are just grasping at straws to avoid applying the standard.

    Also that second reference uses the term accuracy rather than precision. Not good.



  8. Touche Tommy. I bow to the sensei!

  9. Too much mumbo jumbo for me! Just proves you can over analize just about anything. I just look at the ounce fill of 850 down and cut of the bag and I KNOW how warm it will keep me. I will give up my AMERICAN made Western Mountaineering bags when I start hiking in a kilt and wearing a beret! Semper Fi!

    Great article though ..seriously!

  10. I wonder how much it costs to have the test performed? I bet it's prohibitive for the small manufacturers that Earlylite favors.

    I just bought a new bag last weekend and I used the Steve Chase method to evaluate it, since no EN 13537 numbers were available.

  11. I think it will become part of doing business and unavoidable, even for western mountaineering. I think it's required by law in Europe at this point.

  12. Is it the same test with the same sensors in the same position every time? Any standard is a good idea. Anyway moving on I like the French Sleeping bags. WInter bag for sure in the UK. So does a WM Apache compare to a Bloody Mary?

  13. Can't really speak to the comparison but I'd buy the Apache if I ever had to replace my Western Mountaineering Ultralight. It is a very nice bag.

    The videos on the Valandre site are worth watching if you can find them – they've been redoing their site, but they are very informative about the bags' unique footbox and draft collar construction.

  14. Jarra…the cost of a EN13537 test is 2000€ UNIT!

    When you pay that kind of price, believe me you take your time to studdy the result, and compaire it to the kind of info that's out there.

    Martin Rye….the different maniquins used in different certifyed labs, are different in size (surface) and have different numbers of sensors. Test results between labs, can't be compared! It's around +/-5% (5 + 5 = 10%)

    But the worst thing about the EN13537 is, that there's NO control. Anybody can state a EN 13537 result, and claim what ever they like.

    The bottom line is, that the EN 13537 is not credible, and the different "official and controled labs" carrys a united responsability.

    And this is the secondary key reason, why we (Valandre) published a pdf with the official test results.

    For fun, print it out, surf around, and look at the different claims that's out there.

    And have fun!

    Best regards to the community.


  15. Niels – Valandre makes some nice bags. I love how the foot box stands up by itself without compromising down loft and the "marie antionette" collar on your colder bags. Beautiful design. If I could make a suggestion, put your old demo videos on Youtube so we can republish them in outdoor blogs. They're great to watch and very well done.

  16. Prommise, I will look into publishing the videos on youtube.

    But, what about the EN 13537? Don't you think it's time, that the "consumers/users/community" from different blogs, claim to see (and publish on blogs) the official test report?

    The thing that cracks me up is: If "they" payed e2000 unite, why did they not take the time to studdy the report, and draw the conclution as simple, that even my blond whife would understand?

    I have had my nose into this for quite some time now, and believe me….it sucks!

  17. I tried to generate some concern about the test methodology in a previous post… but there wasn't really any pickup amongst other bloggers or the consumer community at large.

    Honestly, I don't think consumers are ready to question such a standard, because there's never been any and they perceive it being good for them as the basis for comparing between manufacturers. Let's face it, if Marmot and REI endorse a standard, there's no going back.

    Instead, I think change has to come from within the outdoor industry (I am a student of human nature and have been on my share of standards committees) and you need to enlist a major brand that has not adopted the standard to force changes to the testing process to make the measurements reliable.

    Find a large manufacturer who is going to be competitively threatened, and they will sponsor push back on wider industry adoption if only to buy themselves time to upgrade their product line. I assume you study the competition, so you should already have a brand in mind. Hope that's not too cynical.

  18. I think you are right Philip, other comments on the NF SnowLeopard being over rated are all I could find quickly. Western Mountaineering and Marmot are reputable outfits, how about Big Agnes or Outdoor Research? Any other suggestions for a real -20 to 0 degree down bag manufacturer? Thanks for the info.


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