When you’re new to backpacking and camping, it’s easy to get overwhelmed by all of the technical specifications involved in choosing your gear. Sleeping bags are no exception. To the untrained eye, a -40F rated, down-fill bag may look super similar to one with synthetic fill that’s rated for 35F. But those factors could make a huge difference with regards to your personal comfort and safety.
Here, we’ll decode the most important aspects of a sleeping bag—how warm the bag is, what it’s insulated with, and how it’s sized—to help you find one that makes the most sense for both your body as well as the season and environment where you'll be using your bag. Once you’ve made sense of the particulars, investing in the right sleeping bag (and sleeping pad) can make snoozing on the ground just as cozy as a night in a hotel room.
The most important consideration when picking a sleeping bag is how warm you'll be while asleep. Sleeping bags come with a temperature rating to let you know what air temperature that sleeping bag was designed for. Sleeping in a 10F bag when it’s 65F out? You’ll be sweating in minutes. Got a 40F bag and it’s only 20F out? Your teeth are going to be chattering all night. If you want to be comfortable, you’ll need to do your research.
In the past, sleeping bag manufacturers develop their own temperature ratings, and there was no good way to objectively compare the warmth of two sleeping bags made by different companies. In 2005, the European Norm (EN) 13537 was released as a standard for all sleeping bags sold in Europe that mandates scientific testing with a thermal manikin to determine an accurate temperature rating for every single bag. The result is a standardized temperature rating, making it easier for you to buy the sleeping bag you need.
It's important to note that women, on average, sleep about 12 degrees colder than men. Standardized temperature ratings account for this by differentiating between “lower limit” (men’s) and “comfort” (women’s) ratings. A women’s bag rated 25F will offer about the same amount of insulation as a men’s bag that’s rated 37F. Conversely, a men’s bag rated 25F will offer about the same amount of insulation as a women’s bag that’s rated 13F.
Down Versus Synthetic
The filling that gives sleeping bags their volume is also what allows them to trap your body heat and keep you warm. Two main types of fill are in use today: synthetic polyester fibers and natural down from geese or ducks. Both synthetic and down sleeping bags have their advantages. Synthetic bags retain their loft when wet and are easier on your budget, while down bags weigh less relative to their temperature ratings and compress to a smaller size.
The type of fill doesn’t affect the temperature rating of the bag, which means a 20F down bag will keep you just as warm as a 20F synthetic bag. The same applies to the quality of down used; a higher fill rating (down typically ranges from 500 to 900) merely provides a measure of how much loft one ounce of down provides. For that reason, a 20F bag made from 500-fill down will keep you just as warm as a 20F bag made from 900-fill down, but the higher-quality, 900-fill down bag will compress smaller and weigh less. Here, the choice you need to make is all about how much space you can afford (and load you can carry) when the bag is rolled up and stashed in your backpack.
Sleeping Bag Sizes
Sleeping bag sizing is more of an art than a science, but they generally come in three sizes: long, regular, and women’s. Long sleeping bags are designed for folks who are up to 6’6” tall; regular fits up to 6’; and women’s bags are sized for people 5’6” or shorter. To avoid feeling constricted, long bags will also tend to be wider at the shoulders relative to their length and women’s bags will tend to be wider at the hips.
Don’t limit yourself to the sleeping bag that matches your exact height, though. We recommend trying a few and selecting what's most comfortable. But be aware that if your sleeping bag is too large, you’ll be slightly colder, as all that extra space inside the bag is filled with air rather than insulation. And if a bag is too small, you’ll be cramped, uncomfortable, and (in some situations) also slightly colder, as a tight fit compresses the insulation, effectively reducing its loft and warmth. It’s also worth noting that long bags tend to both cost and weigh slightly more than their regular-sized counterparts.
Now that you know exactly what you need in a perfect sleeping bag, here are a few of our favorite examples. They'll all keep you warm, comfortable, and ready to tackle the next day’s adventures.