Picking out a sleeping bag is no easy task. Mummy style or rectangular? Down or synthetic? Hooded or open? The options are endless even before you start throwing temperature ratings into the mix. However, temperature rating might be the most important consideration of all. The right sleeping bag will keep you more comfortable, and could even save your life. Knowing how to read a sleeping bag temperature rating will make finding that perfect bag much easier.
What Sleeping Bag Temperature Ratings Mean
Let’s say a sleeping bag says 30°F on the label. What does that mean, exactly? Generally speaking, the temperature rating of a sleeping bag represents the coldest outside temperature at which the sleeping bag will keep its occupant comfortably warm. Essentially, a 30°F sleeping bag should keep you warm as long as it’s 30°F or warmer outside.
That being said, the world of sleeping bag temperature ratings is a bit like the wild west. There are no real rules, although there are some basic standards that most—but not all—sleeping bag manufacturers have adopted. Those standards are known as EN (European Norm) or ISO (International Organization for Standardization) ratings.
If you see an EN or ISO rating on a sleeping bag, that means the sleeping bag you’re looking at has been lab-tested under a standardized set of conditions. These ratings are very helpful for comparing similar sleeping bags from different manufacturers. Most sleeping bags have EN or ISO ratings in both Fahrenheit and Celsius, and may have as many as three different numbers:
- “Comfort” rating, which is the lowest temperature at which one can sleep comfortably through the night.
- “Lower Limit,” which is the lowest temperature at which it’s possible to sleep for eight hours without waking.
- “Extreme” rating, which is essentially the lowest temperature that one can withstand, without risk of hypothermia, for six hours.
Knowing How To Read A Sleeping Bag Temperature Rating Will Help You Choose The Right Bag
Most major sleeping bag companies in the U.S. have adopted either the EN or ISO standard, including The North Face, Marmot, REI and Mountain Hardware. That makes it relatively easy to assume that the ratings you see on these sleeping bags are lab-tested for accuracy.
Of course, real-world weather doesn’t always match laboratory conditions. When you’re picking out a sleeping bag, it’s important to choose a bag that’s designed for the climate and conditions you expect to be exposed to. It’s also worth keeping in mind that, while there is a sleeping bag for every situation, no single bag can realistically offer year-round comfort.
Summer/Low-Elevation Sleeping Bags
Summer sleeping bags have temperature ratings above 32°F. They’re great for camping trips in warm climates and low elevations, and backpackers tend to favor summer sleeping bags because they are lightweight. Many summer bags can realistically be effective in mild spring and fall weather too, but others have temperature ratings as high as 55°F, and should never be relied upon in to keep you warm in cold weather.
Three-Season Sleeping Bags
There’s really no such thing as a one-bag-fits-all scenario. No one sleeping bag can get you through all seasons and climates comfortably, but a three-season sleeping bag is about as close as it gets. With temperature ratings that typically range from 20°F to 32°F, these bags are warm enough to provide comfort in chilly spring and fall weather, but not so warm that you’ll overheat in summer.
Winter/Cold Weather Sleeping Bags
For winter camping and backpacking trips, you need a sleeping bag that will keep you safe and warm, no matter how far the mercury falls. Winter sleeping bags are meant for cold weather, with temperature ratings of 20°F and below. Some winter bags even have ratings as low as 0°F, and are ideal for alpine adventures and overnight trips in truly frigid climates.
How to Maximize the Warmth of a sleeping bag
While we all like to think we’re able to prepare for any situation, the simple fact is that we sometimes miss the mark. Sometimes you go camping with a 32°F sleeping bag, and then out of nowhere, a cold front comes through and sends the temperature plummeting well below freezing.
In a situation like that, you’ll want to squeeze every last degree out of your sleeping bag’s temperature rating, and maybe a few extra if possible. There are a few ways you can maximize sleeping bag warmth:
- Sleep on a sleeping pad. A sleeping pad elevates you and insulates you from the cold ground, which can help keep you warmer and more comfortable on cold nights.
- Wear your base layer. It’s a common myth that sleeping bags keep you warmer without clothes on. In reality, wearing a solid base layer, a wool hat and socks, and even a down jacket in serious conditions, will add extra layers of warmth and help your sleeping bag keep you warmer.
Other Sleeping Bag Temperature Considerations
While it’s important to know how to read a sleeping bag temperature rating, it’s also worth keeping in mind that other factors affect the comfort and warmth of your sleeping bag. These include the quality of the materials, as well as the age of your sleeping bag. As years go by, every sleeping bag becomes a little less effective against the cold. There’s simply no way around it.
The shape and fit of your bag matters too. As a general rule, tight-fitting sleeping bags like “mummy” style bags do a better job keeping you warm than loose sleeping bags. A sleeping bag that fits your body snugly may actually keep you slightly warmer than its temperature rating might suggest, while the opposite is true of a roomier bag.
When choosing a sleeping bag based on its temperature rating, remember that your own safety and comfort is paramount. Some people simply seem to run at a warmer or cooler temperature and others, and two people may have wildly different comfort levels when it comes to temperature. At the end of the day, you should choose a sleeping bag that keeps you at a temperature that feels good to you.
Photo by Jack Sloop
Richard CorriganRichard Corrigan has been writing about outdoor adventures, gear and travel for more than 10 years. His work has been featured by USA Today, 10Best.com, Next Luxury, and Gone Outdoors. He lives in Upstate New York, and If he isn't at his writing desk, you can probably find him out in the woods somewhere.
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