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:

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  1. 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!

      • heres a thought .i use infrared imagers all day long. when you scan a woman as she breathes her nose is ALWAYS colder then her male counterpart. ALWAYS. women typically breath at an increased rate over men and this increase of breathing over time, especially in women play a role in how fast they cool down compared to men. Women will chill quicker then a man while not exerting themselves. I have played with this idea for some time now and it makes sense. the cold air breathed during -temperatures at an in creased rate over men explains the findings on this chart.

  2. 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.

  3. 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 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.

  4. Thanks Phil for this great information.

  5. I have a -1 degree Celsius bag, with a liner and extra clothing I’m hoping to bring that down to about -8 degrees. You have said the EN number is trustworthy, but later you said that a 0 degree bag is more like a 10. Clarify?

  6. I’d like to do some overnights in the Whites this year. I defer to your experience in leading and taking trips, I just want to make sure I understand what you’ve written. Feathered Friends and WM both seem to have lines of -10F bags and of -25F bags. For guys, you would require the -25F bags on such trips and the -10F would not be sufficient, correct?

    I ask because any way you slice it bags for those temps are expensive, heavy, and large (even if necessarily and understandably so). Just wanted to confirm before setting a budget.

    Long time reader, thanks for all the insights!

    • I’ve simply given up on subzero overnights in the Whites. Much less expensive. It’s also no fun if you can’t sit outside to melt snow and hang out because it’s too fricking cold. You’ll have to consult with other winter leaders about what they require. I’m through leading overnight winter backpacking trips for the AMC because lots of people sign up and most cancel at the last minute. I have a zero degree bag.

      • Thank you, I thought I had seen that preference in other posts but I had to ask. For now I have had good results layering my quilts for near-0, low-stakes outings. Having one 0F bag/quilt would save weight and pack space but I’ll consider that low priority.

        I was sorry to read about your ankle injury, I hope it’s recovering well.

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