Choosing a sleeping bag is about a lot more than finding one that matches your personal aesthetic. That’s because you probably aren’t going to care that much what color your sleeping bag is when you are freezing your little toes off in the mountains in the middle of the night. The only thing you are going to care about then is that your sleeping bag is warm enough to get you through the night.
The best sleeping bags are the ones that you chose for that specific adventure, based on how far you are going to carry it (weight) how cold you expect it to be (warmth / insulation) and what kind of performance you are looking for (fill type & extra features).
In this guide, we are going to review the most important considerations for choosing a sleeping bag, paying particular attention to sleeping bag ratings, what they mean, and how to navigate the immense selection of sleeping bags that are on the market today…
“Comfort” and “Extreme”: The Two Sleeping Bag Ratings Your Need to Know About
Anyone who has spent even a few minutes looking for a sleeping bag can tell you that just about every one of them is presented with two different temperature ratings in the product description. The first is comfort, and the second is extreme (or sometimes lower limit). Knowing the difference between these two ratings can go a long way towards keeping you warm and comfortable in the wilderness.
The Comfort Rating is generally the first number that is presented with sleeping bags. This rating shows the ideal exterior (outside) temperature for someone who is going to be sleeping in that bag. As an example, a sleeping bag with a comfort rating of 34 F is going to be pretty warm and comfortable as long as the temperature doesn’t dip too far below 34F.
If a sleeping bag is only presented with one temperature rating, then it is safe to assume that it refers to the comfort rating and not the extreme rating. In many cases, the comfort rating is the first number that you will see displayed on women’s sleeping bags as well, though this varies significantly by manufacturer.
The Extreme Rating or Lower Limit Rating is going to be a lower number than the comfort rating in every case. That’s because it represents the lower temperature end of what is going to feel comfortable. Any outdoor temperatures below the extreme rating might lead to a cold sleep indeed, unless the bag is paired with a liner or additional clothing.
Should I Pay More Attention to the Comfort Rating or the Extreme Rating?
Here’s the thing about comfort ratings: they not only vary by manufacturer, but they will also provide different levels of warmth based on your personal sleeping preferences. As an example, if you are the kind of sleeper that runs a bit hot and is kicking the blankets off in the middle of the night, then the extreme rating is probably the one that you want to use as a guide.
On the other hand, if you are the kind of sleeper that gets cold in the night and needs extra blankets at all times, you should use the comfort rating to make your selection. In other words, you do not want to choose a sleeping bag with a comfort rating lower than the temperatures that you expect to be in, unless you are augmenting your bag with a liner, additional clothing, or a down camping blanket.
Long distance backpackers have a few more considerations when it comes to shopping for a sleeping bag. Being out in the wilderness for extended periods of time can expose you to unexpectedly cold temperatures, not to mention cases of the chills or shivers. It is always nice to have something warm to crawl into after a long day of hiking when your body is more vulnerable. While most summertime backpackers are more concerned with weight and pack size, temperature ratings are always a concern.
The real key is finding a temperature rating that works for you, and this does involve a bit of personal research.
How Sleeping Bags are Ranked & Rated
Until recently, all sleeping bags were ranged, tested, and rated in completely different ways that would vary by make, model, and manufacturer. This led to widespread confusion about temperature ratings, and indeed it was a long period of time when you had no idea of one company’s 15 degree bag was going to perform in the same manner as a similarly rated bag by a different company.
Fortunately, the industry got it together (finally) and decided to adopt a more universal system of temperature ratings, allowing the consumer to have more faith that the product they were purchasing was the one that would keep them warm enough when camping.
European Norm Temperature Ratings
The first standardized temperature system was called the European Norm (EN) 13537 (don’t worry about the numbers) and it was first adopted in 2002. Imagine that before that, we were pretty much flying blind in terms of sleeping bag ratings. The EN was updated in 2012, 2015, and 2016, and it is still a reliable method of temperature rating used by many European countries.
One of the things that the EN introduced to the rating system was the average body heat temperatures of men vs. women. Because adult males tend to produce significantly more body heat than adult females, these differences need to be taken into account if you hope to stay comfortable.
The EN established the following four temperature ranges for all sleeping bags:
- Upper Limit – The highest temperature for comfortable sleep for average adult male
- Comfort – The average temperature for an adult female to sleep comfortable
- Lower Limit – The average temperature that an adult male can sleep comfortably without getting cold or waking up
- Extreme – The extreme rating is the lowest temperature at which a typical adult female can stay warm for 6 hours without risking death from hypothermia (the idea being that an adult male would also be able to survive these temperatures for the same amount of time
As you can see, the EN ratings took significant account of the difference between male and female body temperatures, and established their Extreme rating based on survival.
How EN Ratings are Determined
Getting a sleeping bag rated with EN or ISO requires sending the bag to a third party evaluation lab, where it undergoes scientific testing at the hands of experienced professionals. One of the big ideals behind this kind of standardized sleeping bag testing is that manufacturers would not be tempted to lie about the temperature ratings on their products if they had to be evaluated by a third party.
An EN evaluation uses an advanced test dummy with intricate internal temperature sensors. The dummy is dressed like the average camper with a warm base layer (both top and bottom) as well as a pair of knee-high socks. Researchers are able to put the dummy in the sleeping bag and then set the external temperature in the room. Then, they are able to see how long the dummy will stay within average safe temperatures for humans. This leads to a remarkably accurate readout of just how well insulated a sleeping bag is and how warm it is going to keep you.
Make Your Sleeping Bag Even Warmer: Tips, Tricks, & Accessories
Just because your sleeping bag is not rated for the types of temperatures that you might face doesn’t mean that you have to replace it altogether. Here are a few tips, tricks, and recommended accessories to keep yourself warm and cozy all through the night:
Sleeping Bag Liners
Though the added weight and bulk of sleeping bag liners make them unideal for backpacking, they are a great option for shorter camping trips, hunting excursions, or car camping. Still, sleeping bag liners are not all that big or heavy when it comes down to it. Usually made of fleece or other synthetic fabrics, liners are basically an additional, internal layer for your sleeping bag.
Depending on the material of the liner, it can add anywhere between 5 and 15 degrees to the lower temperature limit. They also work quite well for warm-weather camping where not much warmth is required.
Stay Zipped Up
Even a small gap in your zipper can lead to significant heat loss, destroying any thermal insulation capabilities that you bag was designed with. Remember that while you might not want that much warmth when you first crawl into the bag, the temperature is going to continue to drop until just before sunrise. If possible, make sure that gaps and holes in the bag are as sealed as possible.
Keep Your Down Bag Dry & Lofty
This is truer for down sleeping bags than it is for synthetic-fill bags, but keeping your sleeping bag dry is the best way to maintain the temperature rating. The moment a down fill bag gets wet, it can no longer provide the high levels of insulation that this natural material is known for.
It is also important to maintain the bag’s loft, which is the distance between the internal down feathers and the key to down insulation. A good technique for this is to not store your sleeping bag in the stuffed position when you’re not using it … it is best to hang it in your closet or gear room.
