what degree sleeping bag do i need

What Degree Sleeping Bag Do I Need?

Table of Contents

It’s finally time to get a new sleeping bag. Yours looks like it was probably outdated 20 years ago, but it did the job.

As you begin looking for a new bag, you’re hit with a mountain of different options out there. Where to even begin…

The best place to start is by determining what temperature rating you need the sleeping bag to be. Again, even that feels a bit overwhelming. What degree sleeping bag do I need? Should I keep it safe and get something that is rated to 10 degrees? Or will a 40 degree one do the trick?

Put simply, there are a couple of different factors that will narrow down your search for the best sleeping bag for you. Are you a hot or cold sleeper? Is your sleeping pad warm enough for the conditions you will be sleeping in?

Factors to consider to find the right sleeping bag

What type of sleeping bag are you using

Are you using a traditional sleeping bag or a backpacking quilt? Is it a mummy bag or a rectangular sleeping bag? There isn’t a “better” type to use, per se, but it will have a bit of an impact on how you sleep and how warm you stay. Generally, sleeping bags sleep warmer than quilts, and mummy bags are the warmest of the sleeping bag types. I have slept comfortably in near-freezing conditions in a backpacking quilt, so the type of bag plays a part but is not the end-all-be-all.

mummy bag v quilt v rectangular bag

A backpacking quilt essentially operates like a large, wrap-around blanket. They do not have a “hood”; rather, they stop around the neck region. Many models have a cinch-cord closure at the top to prevent them from allowing too much air inside, but you would need a beanie or something similar to keep your head warm on cold nights. Quilts are not fully enclosed, instead the underside is open. Most will have attachment straps to secure your quilt to the sleeping pad, though.

Mummy bags are on the other end of the spectrum. They are designed to be “form-fitting” and to prevent any cold air from finding its way inside. There is little wasted space or material on mummy bags, making them a top option for campers who need to prioritize weight and warmth. A rectangular bag, on the other hand, allows for more movement while sleeping. This makes them excellent for those who move more while they sleep. The drawback of the extra room is that it allows cold air inside easier.

Are you a hot or cold sleeper

There are a number of reasons why someone may be a “warm sleeper“. Ranging from hormones to what you do in the hours leading up to bed to stress. Some of these reasons can be impacted by hiking all day, so chances are if you’re a warm sleeper at home, you will be on the trail as well. Luckily, for warm sleepers, often times nighttime temperatures in the wilderness are cooler than your cozy bedroom at home. You will likely not have to be as concerned with maximizing warmth at night as your cold sleeper compatriots.

warm fire

If you often find yourself putting an extra comforter on your bed at night or you wake up feeling like the heat in your place has gone out, paying more attention to your sleeping bag is going to be more important. A mummy bag that is rated to a temperature a bit below the lowest temperature you expect is going to be a strong consideration. Since sleeping bags work by trapping body heat inside the bag, retaining as much body as possible will be key.

Is your sleeping pad adequate for the temperatures you’ll be sleeping in

Understandably, sleeping bags get all the attention when campers need to stay warm in cold conditions. But sleeping pads play a huge role in staying warm and getting the most out of your sleeping bag’s insulating ability.

Sleeping pads work by slowing down the transfer of heat from your body to the cold ground. The higher the R-Value rating of a sleeping bag, the better it is at slowing down this heat transfer. This works in tandem with a sleeping bag to keep you warm throughout the night. A sleeping pad creates a barrier between you and the cold ground that is wanting to absorb your body heat. And the sleeping bag allows you to better retain that body heat.

Neither is sufficient enough to keep you warm on its own, but together, you will sleep peacefully all night. For your sleeping bag to fully meet its temperature rating, it needs an adequate sleeping pad. A 20-degree sleeping bag can be comfortable in 20-degree conditions, but if you’re sleeping straight on the ground, good luck. I don’t think of these as two different pieces of gear but rather as a holistic sleep system.

ISO and EN temperature ratings

If you have ever gone out for a camping trip with a sleeping bag rated to 30 degrees and felt cold even though the outside temperature is above 30 degrees, you are not alone. You probably felt a bit frustrated and confused, on top of being cold. Manufacturers of sleeping bags do not have to follow any strict protocol before claiming a certain sleeping bag is rated for a specific temperature. Enter the EN and ISO testing protocol.

EN (and subsequently ISO) rating procedures aim to standardize how sleeping bags are temperature-rated. This allows campers to accurately compare products across different brands. Testing is completed by placing a manikin with a long-sleeved thermal shirt and pants inside of the sleeping bag and placed on top of a sleeping pad. The room is then cooled, and the manikin is monitored with thermal sensors to determine how much heat is lost.

sleeping bag in winter

The results of this testing protocol determine 3 main sleeping bag temperature ratings:

  • Comfort

  • Lower limit

  • Extreme

An easy way to think of these temperature ratings is that the comfort rating is the temperature at which most people will be able to stay warm and sleep comfortably throughout the night. The lower limit rating is the temperature at which a warm sleeper would be able to stay adequately warm throughout the night. And the extreme rating is the temperature at which you would be able to survive the night. By survive, I truly mean survive; the ISO protocol puts it as “the risk of health damage by hypothermia is possible.”

When evaluating a sleeping bag temperature rating determined using ISO tests, I generally use the comfort rating. This allows me to sleep comfortably in the expected conditions without having to bundle up excessively every night. Plus, if temperatures drop a bit more than expected, I can still stay out of harm’s way.

Brands are not required to utilize the ISO testing protocol. Most will advertise on their website or on the product page of a specific bag if it is rated using ISO testing.

Summer vs. three-season vs. winter sleeping bags

A lot of backpackers and campers will often refer to sleeping bags in categories. For example, you may hear someone describe a bag as a three-season sleeping bag. So where do these categories fit in? These are far more subjective terms, so take them with a grain of salt.

Generally, a summer (warm-weather) sleeping bag is one rated at or higher than 40 degrees. These are ideal for trips during the warmer months at lower-to-mid elevations. Additionally, trips in low desert areas during the cool months may fall into this category depending on the specific location.

Three-season sleeping bags have temperatures between 20 and 40 degrees. Many sleeping bags fall into this category and are ideal for a wide range of trips. Three-season bags work for summer trips into the high mountains and almost year-round at lower elevations, excluding summer months in low, hot deserts.

The least common are winter sleeping bags, or anything rated below 20 degrees. Suitable for shoulder seasons in high elevations or winter camping elsewhere.

FAQ

If it is a mummy bag coupled with a high R-Value sleeping pad, and you’re a warm sleeper, it may be too warm. But a 20-degree quilt paired with a lower R-Value sleeping bag can be versatile enough to work in summer conditions.

Some brands utilize ISO-standardized testing, while others utilize their own testing procedures.

The temperature rating on the sleeping bag will remain the same, but a more insulated sleeping pad can increase how warm a particular bag can feel. There are many other ways to stay warm throughout the night; the easiest is wearing an insulated jacket and/or beanie.

Conclusion

Determining the right temperature rating for your next sleeping bag can be tough. Should you choose a higher-rated bag to save a little bit of weight? Should you expect the worst and get a lower-rated bag? The truth is somewhere in between. You shouldn’t risk waking up every few hours to your body shivering to stay warm. On the flip side, you don’t need to get the coldest-rated bag you can find “just in case.”

Determine the conditions that you anticipate sleeping in the most: cold nights in the mountains, mild spring nights in a grassy meadow, or warm nights in the desert. This will narrow your search down significantly. As outdoor explorers, we rarely stick to just one type of experience, but consider where you will be the majority of the time. (you may need multiple sleeping bags if you plan to do a full range of trips)

This should narrow your range down to about a 10-degree window. Maybe you’re between a 20-degree and a 30-degree sleeping bag. At this point, consider things like how warm of a sleeper you are and the R-value of your sleeping pad. If you still aren’t sure at this point, you can lean toward whether you value a small weight savings or a little bit of extra insurance on a cold night.

Whether you determine a 40-degree bag is right for you or a 0-degree bag is your best option, put it to good use and explore what is out there!