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Winter Sleeping Bag Temperature Ratings: Words of Warning

EN13537 Temperature Rating Label
EN13537 Temperature Rating Label

Cold and winter sleeping bag temperature ratings – those under 10 degrees fahrenheit  – are not assigned using the new EN13537 sleeping bag standards that many North American sleeping bag manufacturers now use. The new standard has proven unreliable for bags rated below 10 degrees, so most manufacturers rate their bags using the same techniques they used before the new sleeping bags standards were introduced.

That’s a problem for several reasons:

  1. Experience with the new EN13537 standard showed that manufacturers overestimated the warmth of their three season bags by about 10 degrees. For example, a 20 degree bag from a few years ago would be closer to a 30 degree bag when tested with the new standard today. Therefore, it’s probably wise to add 10 degrees to a cold weather sleeping bag that is rated by the manufacturer. For example, a bag rated for 0 degrees is probably closer to a 10 degree bag, and a bag rated for -20 degrees is probably closer to a -10 degree bag.
  2. When manufacturers rate their own sleeping bags, they’re almost always using a MENS rating and not a WOMENS rating. One of the benefits of the EN13537 sleeping bag standard is that it showed that women sleep much colder than men. So if you’re female, you should probably add another 5-10 degrees to the rating of a cold weather bag unless it’s a women’s specific model.
  3. The sleeping bag temperature ratings of cold weather bags listed by most manufacturers assume the you are wearing long underwear (tops and bottoms), socks, you’re sleeping on a sleeping pad with a high R-value (5+ is a good winter minimum), and your sleeping bag is not exposed to the wind (you’re in a tent or a bivy sack.) If you don’t do all of these things in winter, you will sleep colder even if your sleeping bag rating is 100% accurate.

Implications for Winter Backpacking and Camping

I lead a lot of winter backpacking trips in New Hampshire’s White Mountains for the Appalachian Mountain Club and I always interview people who sign up for my trips to see if they have the required gear, experience, skills, and physical conditioning required to complete the hike safely.

At night, winter time temperatures in the White Mountains range from 0 degrees down to -20 below. Since I can’t forecast the weather when I schedule my trips – often months in advance – I require that all of the people on my trips have -20 degree sleeping bags.

Assuming they have all the other gear and clothing required, a sleeping bag with a -20 degree bag will keep a man comfortable down to -10 degrees, and a woman, down to about -10 to -5 degrees. When screening participants, I also try to find out who manufactures their sleeping bag, because manufacturers such as Western Mountaineering and Marmot tend to rate their sleeping bags more accurately, either because they overstuff them with high quality goose down or they test them in refrigerators (called cold rooms.)

However, if someone with a sleeping bag with a 0 degree rating applies to get on one of my winter backpacking trips, I will turn them down. If they’re male, this equates to a 10 degree sleeping bag or a 15-20 degree sleeping bag if they’re female, and that is simply too risky for winter nights in the Whites. On a -15 degree night, they’ll be worse than uncomfortable.

Winter Sleeping Bag Temperature Ratings

Be forewarned:

  1. Cold/Winter sleeping bag temperature ratings are assigned by manufacturers and fall outside the new EN13537 sleeping bag standards.
  2. The temperature ratings on most cold weather/winter sleeping bags are probably 10 degrees too warm.
  3. Women need winter sleeping bags that are 5 to 10 degrees warmer than men.
  4. Most winter sleeping bag temperature ratings assume that you are wearing long underwear including socks, sleeping on a sleeping pad or pads with a high combined R-value, and you are in a tent or bivy sack.

For more information, see:

Updated 2015. 

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  1. Do you take it into account when people include their insulating layers as part of their sleep system? Sleeping in a down puffy seems to be a trend among ULers.

    • If I know someone personally and I know that they know what they are doing,then perhaps. But honestly, they’d be much better off using a vapor barrier liner in this case.

      If it’s someone I don’t know and haven’t hiked with before in winter, then no. I won’t jeopardize everyone else on the trip because someone doesn’t have the right gear and is inexperienced in winter camping. Most UL backers don’t hike in winter, so it’s never been an issue.

      UL backpacking is marginal in the winter Whites. You can use the concepts to keep your load under 55 pounds, but at 20 below and even higher wind chills, you’re happy to bring full winter gear.

      • I can’t speak to the East, but in Colorado there is usually enough snow to use a sled so ultralight is less necessary.

        Do you make an adjustment if someone is sleeping in a quinzee or snow cave? Do you typically construct snow shelters on your hikes?

      • You’d have to because the ambient temperature will go up to about 30 degrees. The problem is that you can’t count on being able to build one, especially in New Hampshire where the snow depth limits the amount of snow at your disposal to build a shelter.

      • Yeah, love those 0F degree days, a storm moves in dumps 2″ of frozen rain then goes back down to 0F. :-(
        Never go anywhere in the NE back-country without your ice crampons.

      • A sled in the Whites will pull you off the mountain.

        People seriously underestimate New Hampshire, particularly in winter. Compared to Colorado it’s colder, wetter, less snow depth, and a lot steeper. (More likely to be out in a storm, too.) Thicker air and a bit less in the way of avalanche terrain are about the only easier bits. Approaches are often shorter in terms of distance but not in time.

        AMC trip leader protocols are conservative and seem downright overkill to those with mountain experience elsewhere, but there are really good reasons why people have settled into them. The usual story: http://home.earthlink.net/~ellozy/Bonds.html

        (formerly of New England, currently northern New Mexico)

  2. Point 4 in your be forewarned section.
    I never realised that manufacturers rated sleeping bags this way. Its ridiculous, how do you set a std when there are so many variable options to clothes, mats, tents, ground topography etc.
    I never realised this and will be asking my sleeping bag maker how they test theirs. Thanks

    • I’m surprised Alan. One, that’s an integral part of the EN13537 testing process which was developed in Europe and Two, who would sleep in a cold room if they weren’t on a sleeping pad?

  3. Yes, there is still a large variability between manufacturors even with the new standard. They tend to “round off” numbers to their benefit. It is rare to see a bag rated to -5 when -10 is a more attractive number.

    The sleeping cloths, item 4 above, really is a huge variable. In summer, I can use a light 40F bag with light long johs and a shortie pad. To take this down another ten degrees, I simply use heavy weight long johns and a thicker, full length pad. Would I be better off with another bag for every ten degrees, weight-wise? Does this complicate my packing system to the point of needing a second pack? Yes, another, thicker bag will. Doubtfull whether the few cubic inches will effect your pack between long-johns, though. I expect the manufacturors know the difference, but rarely state it. Though, some do state the MAXIMUM temperture to use a bag. You should know that a large difference means they are likely playing the “numbers” game on the tags. A narrower range means a better bag, since HOT and COLD are oposites, If you have warmth, it will make you too hot, sooner, hence a narrower range. A wide range will tell you more about a bag(and tests) than provided they don’t “round off” drastically.

    Is the system better than the US system of simply assigning numbers that will work based on other bags being sold? Yes. At least some attempt is being made to standardize things. It started out with good intentions, but… At least they use a standard reference for down fill. 800FP is the maximum in EN lingo. I have seen 850, 900, and even 1000 fill power bandied about. These are meaningless. An EN800 fill is max for fluffiness. You *can* add by adding stiffeners to the feathers. Do you count this? What happens if/when the stiffener wears out or causes breakage of the feathers that much sooner? Manufacturors are playing with this in the effort to sell you cheaper 600fp down, not the good EN800 stuff. The “dry down” resists water. But, who gets their bags wet? Not me….not if I can avoid it anyway. I TRY to keep it dry because I KNOW I have to sleep in it. They never talk about the second night.

    • Many manufacturers have stopped “rounding” the numbers off and now label with the EN13537 test rating. Sierra Designs was the first to rename their bags in the manner. But since the standard tests don’t work under 10 degrees F, below that it’s anybody’s guess what the “true” rating is.

  4. If you look at the detail-section from Mammut: http://www.mammut.ch/nb/productDetail/241000942_v_195/Sphere-UL-Winter.html

    is this more satisfying?

    If I understand your statement, it is the lack of reference to EN13537 that is the problem?

  5. Great info. Lots of food for thought. I wonder what rating technique the US military uses to rate its MSS . . .

  6. Could we get some reference to standard test failing at 10 degrees, I´ve heard that the failing part is just something that US sleeping bag manufacturers came up with, since the EN13537 revealed that their bags insulation values where highly over rated..

    • A member of the standards committee sent me the outdoor Industry associations meeting minutes which cover the issue and briefed me on the topic. I’ve known this person for several years, since I’ve written about the standard extensively, and they are an expert source.

  7. http://www.mammut.ch/images/Mammut_Sleep_well_pt1_E.pdf

    EN 13537 and Extreme Low Temperatures

    EN 13537 does not apply to sleeping bags for extreme low temperature use. The thermal
    resistance tables in EN 13537 suggest that sleeping bags which claim comfortable sleep
    below – 24 °C would be outside the standard.
    The principle reason for exclusion of these temperature ranges is that the sleep mat
    and clothing used are very different to those defined in EN 13537. Defining such a test
    would be difficult as there are different clothing conventions for polar travellers and
    mountaineers. For example, polar explorers often use vapour barrier liners and mountai-
    neers often sleep with a full down suit inside the sleeping bag. Secondary reasons are
    the effects of sweat and respiration. Heat lost through respiration becomes an important
    factor in very cold conditions. Also, moisture from respiration and sweat reduces the
    effectiveness of the insulation.
    It is theoretically possible to create a customised test based on EN 13537 that is modified
    to use the exact garments and sleep mats. It is also possible to use a sweating manikin
    and an exceptionally cold climate chamber. Both of these would be expensive to test and
    difficult to repeat in different laboratories. However, the data from a standard EN 13537
    test is still a valid comparison between sleeping bags of different designs and from dif-
    ferent manufacturers.


  8. There are sleeping bags ostensibly made specifically for women?

    Kidding, right? Please.

  9. Ole and Eric put out great links to Mammut and their winter bag that shows how the EN standard works as a “RANGE”. Versus the US standard that provides a single number.

    Mammut Shere-UL-Winter
    max. temperature to EN 13537 in Celsius 15
    Lower comfort temperature for women to the EN 13537 in °C -5
    Lower comfort temperature for men to the EN 13537 in °C -11
    Extreme temperature to EN 13537 in Celsius -32
    US Temperature in degree Celsius -15
    US Temperature in Fahrenheit 5

    The EN “RANGE” is based on an average; age, height, weight and body surface area. The only difference between a man and women is that the average height, weight and surface area is DIFFERENT.

    Standard woman (25 years old, 60 kg, 1,60 m, 1,62 m2 body surface area)
    Standard man (25 years old, 70 kg, 1,73 m, 1,83 m2 body surface area)

    The US Standard provides on a single number for the temperature rating of a sleeping bag, which is lower than the EN “COMFORT” temperature.

    The variables for staying warm below freezing are exponential. The EN standard shows a “RANGE” that includes the risk of cold weather camping as “EXTREME”. Precautions and experience beyond the sleeping bag alone are needed to insure safety at these low temperatures. In order to get a “COMFORT” rating below 0F with the EN calculations and test parameters (mattress and 1 CLO outfit) is difficult, and makes the bag 3x the size and weight.

    My name is Jim Giblin; I work for Cascade Designs and I am the Sub-Committee Chair for ASTM F08.22 on Tents, Backpacks and Sleeping Bags. The views expressed on this website/weblog are mine along and do not necessarily reflect the views of Cascade Designs, Inc.

  10. Philip,
    Thanks for proving such an abundance of information on your site! Over the years I have found the information that you provide most helpful.
    I have reviewed the winter checklist of the ADK winter school and my question is if you were to keep the heavy down jacket and pants, remove the -20 bag and replace it with a WSM -10 or 0 and add a VBL clothing system would that be sufficient? I have read Andrew Skurka’s lists and it seems like it worked for him during his multi month adventures. Not sure if this system is possible in the Adk’s and Whites.

    • I would be cautious about trying to adapt Andrew’s VBL clothing outfit to the ADKs and Whites. Andrew tends to move very fast – ski/walk/run and generates a lot of heat. The whites and dacks defy that pace of travel. If you go down that route I would suggest a lot of short 1 night experiments, with failsafe backups, and not an extended journey.

      I’ve messed around with various types of VBL in Northeastern Winters and have found that VBL socks/reynolds oven bags are the VBL layer the works best for me so I can bring lighterweight montaineering boots without removable liners. A sleeping bag VBL is just too uncomfortable and foreign (for me), but it is one proven way to reduce your insulation needs if you can stand to sleep naked in one.

  11. Back in 1972 or thereabouts, when Backpacking Magazine was a real magazine on backpacking and not a vehicle for advertising revenue, the Publisher and owner at that time also had issues with ratings for Sleeping Bags and their claims.. So the Industry has basically dodged the bullet on accuracy for over 41 years. Same with equipment weights, Back then BP actually used to have a monthly section with the Manufacturer’s claim as to weight versus the BP scales and well the Manufacturers sure took some literary license in their weight claims. The Editior also frequently attacked the “toughness” of the gear. Back then my pack for a weekend could weigh in at near 55 pounds, now 21 pounds cause I bring more solid food versus dehydrated. After 41 years of reading all of it from both sides and my own experiences, what I feel that there is no “Standard male or female” and the temperture ratings cannot be accurately gauged as to the amount of heat your body is going to produce that heats up the inside of your bag, and that is a huge problem that nobody will ever be able to anticipate or accurately measure. I mean they’ve been trying for 41 years, even built Hi Tech Mannikins in Laboratories trying to find out, the MIlitary has tried and failed. It just cannot be done. Only your personal testing will surfice. I know that bare skin, in a 20 deg rated 650 down filled sleeping bag with an outside the tent temperature of 19 degrees I will be overly warm in a Down bag. Put me in a 20 deg rated man made insulation filled bag and I am very cold at 38 degrees and only after having put on my long johns and a Down vest and I am happy. I also believe distance walked and altitude cause my body to reject certain temperature ratings. I know at 11,300 feet in August, a man made insulated bag rated at 20 deg’s will NOT keep me warm, but a Down filled bag will. Why I haven’t clue, I just suffered through the “test” and didn’t make the same mistake the next trip. At Sea Level in the Mojave Desert in January, Down is too hot but Man made is just right. Same with Fleece Clothing vs Down, I do not have to wear “layers” upon layers to keep warm at 11,300 feet in August in Down, but with Fleece it is long underwear and four layers deep and I still feel a bit of chill. So my advice is to purchase a varieity of bags from a Reputuable dealer with a flexiable product return poiicy, use a sleeping Bag liner and test a couple of bags. If you test it in your backyard I would suggest you take a six mile hike around your neighborhood, eat the same trail food as you plan to and then test the bag. I currently own seven bags that I have accumulated over the years from minus 20 rated to 40 degree rated and now just use two, Mountain Engineering Goosedown, and the very reliable Blue Kazoooooooo! I have the current Military issue two bag system with Goretex Bivy cover and used it last year while hunting in a winter camp three feet from a glowing campfire, I was very warm, but, it weighs in at 12 pounds….

  12. “Women need winter sleeping bags that are 5 to 10 degrees warmer than men.”
    So, 98.6 plus 5-10C?

  13. For comfortable sleeping, in a really warm bag, with a fully down-protecting vapor barrier, adjustable layering and a built-in insulated pad, check out Stephenson’s Warmlite bags. I have slept in the snow in NH many nights in their bags without any discomfort. May not be UL however.

  14. ok…and synthetic or down for multi-day winter hike in NE?

  15. Just curious, why synthetic for more than 7 days? My down bag is only rated for 40, so when the weather starts to turn I go synthetic anyway.

    • In winter, you sleep with all of your wet gear, including your boots, to help them dry and prevent them from freezing at night. That, together with your body perspiration starts to degrade the loft and insulation ability of the down. One way to prevent this is to sleep in a vapor barrier liner. But most people never stay out more than a few days in winter anyway.

  16. Why not assign R values to sleeping bags, like they do to sleeping pads? There’d be no personal interpretation of, no assumption of clothing, no mixed up rating values.

  17. Hi, I was wondering if using 2 40 degree sleeping bags would be ok in a 36 degree weather, tent, and pad. 10-20 degree sleeping bag takes most of the space in my backpack and the closest sporting goods store has nothing slimmer or smaller.
    Thank you

  18. Hi Phillip. I cam across your post, when I was looking at how I should choose a winter sleeping bag. I was looking to get a -30F sleeping bag from Mountain Hardwear. It’s a synthetic bag. 

    To better understand this, let’s say I decide to purchase the bag, sleep in it with temperatures going down to -20C to -25C with wind chills some times bringing the temperature down to -35C. Its not always like this as the temperatures usually stay at -15C to -25C here in Ontario, but on those few odd days, it does come down to that. 

    From what I understand is that, a sleeping bag that is rated at -30F (-34C), actually feels like a -20F (-28C) sleeping bag, which means I won’t be sleeping comfortably at -30F (-34C)? Or is it the other way around, and that I can comfortably sleep because the temperature inside the sleeping bag has been raised to about 10F higher making the sleeping bag feel like a -40F bag.? ?

    • Note quite. The point of this post is that you can’t trust the temperature rating on a subzero bag because there’s no standard way to measure it. You haven’t indicated your sex, but the gender difference still pertain. BTW, Wind chill doesn’t reduce temperature (just it’s perception) and you’re probably not sleeping in the open either.

      • Hi Philip, sorry for the late reply. I’m a male, 25 years of age. I see now. Everything is starting to make sense now.

        I also read through Therma-A-Rest’s post on how to choose the right sleeping bag (thought it was informative). Apparently from what they found out, is that there’s not much of a difference between male and female, when it comes to winter camping. The idea that females sleep colder than males is apparently a myth. It all depends on the weight and age of a person and what they ate, when they ate, are they sleeping with a hot water bottle and such. If both were the same age and weight, both would relatively sleep at the same temps, whereas if a male weighs more and is a bit younger, a male may sleep warmer. But of course it all depends on the person and how well they handle it.

        I work in retail in a outdoor store, here in Toronto, ON. I was trying to understand and wrap my head around on how a person would stay warm. Or how I would stay warm if I attempted to do winter camping. Your post helped me a lot to better understand ratings. Thanks a lot man!

  19. Question. I am looking at the Western Mountaineering Sleeping bag called the “Versalite” vs the Western Mountain Sleeping bag called the “Antelope”. The versalite is 1 pound lighter and you get 1″ left loft and it is $100.00 CHEAPER for a 10 degree bag. The Antelope is 1″ more loft, 1 pound more down and 100.00 more expensive. Q. Is it worth the extra 100 bucks for more loft and lighter to backpack the PCT? Is it worth going with the lower weight for a cheaper price and not as much down in it? Thanks…Mig

    • I would contact Western Mountaineering and ask them what the EN13537 ratings are for the two bags in question. That will tell you which is warmer. The depth of loft is only one factor in determining the warmth of a bag.

  20. I do a lot of snowboarding in Maine and northern Vermont. I have a valandre Thor sleeping bag and sleep in my car in the parking lots for different mountains. I also hike and do different backcountry riding. I highly recommend this bag. I’ve slept in -40 degree nights up in Canada and stayed pretty warm. Sometimes I start to get cold around 4am. If anyone has any tips or questions for that matter I would be happy to answer them, and also appreciate your suggestions.

    • Jayce,

      I understand from sectionhiker.com that you sleep in a Valandre Thor in sub-zero conditions on various mountains you ride. I’m interested in Valandre and am familiar with the “Shocking Blue,” a contemporary to the “Thor” model. But I’m trying to find the original specifications for a discontinued model called “Valandre Blue 600.” I surmise the “600” refers to down-fill capacity used at the time, and suspect the “Blue” designation may distinguish it as a predecessor to the current “Shocking Blue” model which comes standard with 800 down fill. QUESTION FOR YOU: Can you (or anyone reading this thread) refer me to a URL that features this “Valandre Blue 600” model, its technical specs, or even a year of introduction?

      Any help you can give is appreciated.

    • This happens to everyone. Eat something. It will rev up your metabolism and help you generate more body heat. Something fatty is ideal, like cheese.

      • Thanks, I will have to try that. In the car it’s not bad (kind of cheating) I can turn on the heat. But on the mountain is another story. I like to dig out a little cave to sleep in and block the wind. It’s crazy how warm it can be in that bag, in a snow shelter, on top of mountain.

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