Understanding Sleeping Bag Temperature Rating

sleeping bagA sleeping bag is one of the most important pieces of outdoor gear that you will ever own. It’s right up there with your tent and your hiking pack. A good sleeping bag makes the difference between a good night’s sleep and a restless night of shivering. But how do you choose a sleeping bag?

Size and weight are important factors, of course. Maybe you have a preference between down sleeping bags and synthetic sleeping bags. Perhaps price is an important factor for you, too. But most importantly, you need a sleeping bag that will keep you warm. Choosing a sleeping bag that’s warm enough for you isn’t as straightforward as you might think, however.

Here’s some information to help you understand sleeping bag temperature ratings.

What is a sleeping bag temperature rating?

A sleeping bag temperature rating indicates the temperature at which the manufacturer recommends the bag be used in. This rating is often included in the name of a bag. The Marmot Trestles 30, for example, is a bag intended for around 30° F.

It’s important to understand that sleeping bag temperatures ratings aren’t entirely accurate. It’s just not possible for these ratings to be exact. A sleeping bag temperature rating is more of a ballpark figure, and this is true for a couple of reasons.

There isn’t a required standard for measuring temperature ratings.

While many sleeping bag manufacturers use the EN 13537 standard (more on that later), it isn’t required. This means that it’s up to the manufacturer to decide how to test, measure, and rate a sleeping bag for warmth.

But even if a sleeping bag is tested using the EN standard, there’s still a bit of wiggle room in the temperature rating.

People respond to temperatures differently.

Comfort is subjective, and people handle temperatures differently. You’ve probably been sitting around a campfire where one of your friends is comfortable in a T-shirt while another complains about the cold despite being bundled up in blankets.

You could give two different people an identical 30 degree bag on a cool night with a 35° F degree low, and one of them won’t be able to sleep because they’re cold, while the other sleeps like a baby.

Some folks generate more body heat than others, some acclimate to the cold more easily, and some people can just handle cold temperatures better than others.

Men and women are different, too, in how much they feel the cold, and not coincidentally, it depends on body size. So, you can see why temperature ratings aren’t entirely precise.

EN 13537 Standard

While temperature ratings aren’t perfect, they are better than nothing; and the EN standard is widely used and research-based. The EN rating system is a test with exact criteria, and it’s conducted with thermal manikins.

With the EN rating, you get a more in-depth look at how the bag will hold up in given temperatures. It doesn’t mean a 30° F bag will keep every person ever cozy in 30 degrees; instead you have upper limit, comfort, lower limit, and extreme temperature ratings.

  • The upper limit rating is the temperature a “standard man” can sleep at without excessive perspiration.
  • The comfort rating is the temperature a “standard woman” can sleep comfortably in a relaxed position.
  • Lower limit is the temperature a “standard man” can sleep in a ball for 8 hours without waking.
  • The extreme is the lowest temperature a “standard woman” can sleep at for 6 hours without the chance of death. However, it doesn’t exclude the chance of frostbite.

Check your sleeping bag before you buy it to see if the bag was tested using the EN standard, and see where the ranges lie.

Hot sleepers and cold sleepers

While it’s nice that the EN system makes temperature ratings regular, they’re still very much subjective. It’s hard to know what a “standard” man or woman is and whether or not you would qualify.

And regardless of gender there are hot sleepers and cold sleepers. Hot sleepers typically produce lots of body heat in the night and cold sleepers don’t.

It’s important to know which type of sleeper you are before you choose your sleeping bag. If you are a cold sleeper and you’re expecting to sleep in 40 degrees, you’ll probably want a bag that’s rated at around 3o degrees if not lower. If you’re a hot sleeper, that 30 degree bag might be too warm.

Men’s sleeping bags and women’s sleeping bags

Another thing to keep in mind is that women’s sleeping bags are typically rated to be warmer than men’s sleeping bags.

For example, the Women’s Trestles 30 from Marmot has a comfort rating of 33 degrees, while the Men’s Trestles 30 only has a comfort rating of 42 degrees. That’s nearly 10 degrees difference between two bags that are labeled for the same temperature.

Other factors that affect sleeping bag warmth

It’s not just the sleeping bag temperature rating that you need to pay attention to. The clothes that you wear, your sleeping pads R-value, the type of shelter that you’re in, and how your sleeping bag fits all play into how warm you will be in a bag.

The best way to choose a sleeping bag is to stop by Uncle Sam’s Safari Outfitters, or your local outdoor gear store, and talk to the staff. We’d love to help you find the bag that’s right for you!

2 Comments

  1. […] of course, you want to have a good sleeping bag. Keep in mind whether you’re a warm or cold sleeper, so you know how warm your sleeping bag […]

  2. […] You have to have a sleeping bag. Your sleeping bag will provide most of your warmth, so you want to make sure that your bag is adequate. Sleeping bags come with temperature ratings, but a 30 degree bag won’t necessarily keep you warm in 30 degree temperatures. Know whether you’re a warm or cold sleeper to determine how warm your bag should be. […]

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