Is there any upper temperature limit for a given sleeping bag?

I'm actually shopping for a new sleeping bag and am a bit in doubt about a question that I do not find treated anywhere: By investing an arbitrarily huge amount of money I can buy a sleeping bag to sleep snuggly down to -30° C and even below. But what about the other side? Let's say, I buy a sleeping bag with a comfort rating of somewhere between 0 and -10° C, can I use it also in a warm summer night? Or is there some temperature where it will be just too warm to use it even with zipper fully opened and used more like a blanket?

I'm aware of the fact that I will carry more weight and volume than necessary for an insulation that I would not need. I'm just interested about the comfort at the warm end of the temperature scale. So if I buy a bag with some reserve for cold fall or winter nights, will it be unusable in summer or only not the best choice I could have had? If it is unusable above a certain temperature is there some rule of thumb that says something like "a bag that has a comfort rating of X won't be of use for temperatures roughly Y degrees above that X rating."

• and more volume! :)
– ppl
Mar 6, 2014 at 23:04
• This is a very subjective question and I'm not sure it actually has an answer other than "Do what's comfortable and practical." The lower temperature limits are there because it's much more difficult for a body to stay warm, by maintaining a safe and usually comfortable temperature (more insulation for lower temps). When it's hot you'll shed any insulation long before your body temperature gets too hot so an upper limit rating isn't really necessary. Know your own body. Mar 9, 2014 at 2:02
• @manoftheson I'm aware of the fact that is strongly dependent on my own body how warm a bag I can bear! So basically my question boils down to "If I buy a bag that has some reserve for cold fall or even winter nights, will it be totally useless in summer or will it just be not the best option I could have had?" Mar 10, 2014 at 9:43
• Ok I understand more where you're coming from now. I thought you were looking for an actual numerical threshold of where it's too warm to use a given sleeping bag. It might help to clarify your question a bit. But here's what I do: I use a lightweight, 45'F bag for summer because my winter bag, which is 15'F, is just too hot in temps above 55-65'F. I also use a thin synthetic sleeping bag liner that I can use by itself if my summer bag is still too warm. I'm also a "hot sleeper." But to each his own as they say. Mar 10, 2014 at 16:33

I have not encountered a situation where a sleeping bag was "too warm" and I was unable to do something about it.

I've gone backpacking in the mountains where it was 70 at night one day, and the next day, several thousand feet higher, it got below freezing. At night in the heat, I pretty much just used my sleeping bag as a blanket with the zipper all the way open.

However, you do risk the possibility of being in the sleeping bag, falling asleep comfortably, but being far too warm, and waking up later drenched in sweat.

There is an Upper Limit and Here's Why

There are in fact times when a sleeping bag can be too warm. Although leaving the bag unzipped allows heat to radiate away from your body upwards, the insulation between you and the ground significantly reduces the amount of heat that your body can dissipate. How far you sink into the insulation also has a significant impact, so thinner bags will do well at higher temperatures than thicker ones, even if they have a similar rating. Sleeping on a stack of wool blankets is comfortable at almost any temperature (assuming your skin doesn't react to the wool).

What is the Limit?

What too warm of a temperature would be depends on both how low your bag is rated and how far you sink into the insulation. My -20F bag gets uncomfortable above around 65F, whereas my 35F bag is good until around 75F, assuming low humidity. Higher humidity raises the range for the heavier bag and lowers it for the lighter one.

The Solution

Although the problem is real, the solution is extremely simple. Place a cotton sheet on the bag before laying down. The cotton sheet pushes down the insulation and creates gaps for increased airflow, which helps your body regulate your temperature.

• If you are just simply laying on your sleeping bag, and it is so hot outside that doing that is a problem, you can always just lay right on your sleeping pad or tent floor. Practical issues of hauling a bunch of unnecessary weight will come into play before the temperature does. Mar 9, 2014 at 5:23
• I agree, however, the question was specifically regarding upper temperature limits for sleeping bags, not best practices for warm weather sleeping. Mar 10, 2014 at 15:21

I went out once with a bag that was too warm. Sometime in the night I woke up covered in sweat and freezing cold! My sweat had soaked the down, completely ruining its insulation properties.

If you want to go outdoors all year round then you just have to accept that you'll be buying twice the gear. A summer pack and a winter pack. A summer sleeping bag and a winter one. Summer boots, shoes or sandals and winter boots.

What hasn't been mentioned so far is that different materials have different ranges. A down sleeping bag is usually comfortable over quite a larger temperature range than a synthetic one. I have a flimsy synthetic liner bag (they are also available in silk, but this one claims to be microfiber) that at least avoids draft when the regular bag is better open because of warmth. My liner bag washes easily as opposed to the down bag, so it also helps keeping the main bag from getting grimy.

Just stating the obvious, you should consider where and when you are hiking. Death Valley and the Appalachin trail offer extremely different environments. I have multiple different sleeping bags for different occasions. In the summer, I generally use a 45 degree down bag. In spring and fall, I tend to carry a 30 degree bag, and in the winter I carry a 0 degree downfilled bag.

These hikes are generally in the Smoky Mountains where in addition to moisture from the environment, perspiration is also a factor. Unzipping the bag is an option but so is sleeping with multiple layers of clothing. I prefer to stay as dry as possible when sleeping.