Have you ever spent a cold night in your sleeping bag wondering why you are cold when you’re sleeping in a bag that is properly rated for the temperature outside?
A lot of backpackers and campers have this problem and blame their sleeping bag for it, when it could be caused by a number of other, easily correctable, factors. It’s quite possible that replacing your sleeping bag will still not solve the problem. I can speak from experience!
You need to understand that your sleeping bag is just one component in an integrated sleep system. At a minimum your sleep system includes a shelter, a sleeping bag, and a sleeping pad. It probably also includes long underwear to help keep the inside of your bag clean and a fuzzy hat or balaclava to keep body heat from escaping through your head. Depending on the weather and the type of shelter you use, your sleep system might also include extra insulation, a second sleeping pad, a vapor barrier bag, a down or synthetic vest, wool socks, insulating booties, chemical heat packs or even a well-sealed bottle of hot water. In a pinch, you can use every single ounce of your gear and components from your surrounding environment to extend the temperature range of your sleep system.
The art of sleeping warm requires that you understand how all of these components work together. This requires a little experimentation to better understand how the different variables in your system interact. Expect a few botched experiments.
Here is an example from my own experience to illustrate what I mean:
I decided to do a 25 mile section of The Long Trail in early November. Temperatures were expected to drop down to the thirties. I drove up in the evening, hiked in from the road a ways, pitched camp, cooked dinner, and went to bed at sunset (5pm). Elevation was about 1,000 ft. Winds were relatively calm.
My sleep system included:
- an 800 fill goose down REI Kilo sleeping bag rated for 20 degrees
- Hennessy Hammock, Backpacker Ultralight Asym
- Jacks R Better 8ft x 8ft tarp
- Jacks R Better Nest – an 800 fill goose down hammock under-quilt
- Patagonia Capilene 3 long underwear
- Cocoon Polarguard vest
- fleece cap
- an emergency space blanket
I knew this was going to be marginal but it was worse than I expected. The temperature went down to 32 degrees. I was freezing until I broke out my mylar bivy and used it as a vapor barrier in my sleeping bag. I got drenched in sweat but at least I was warm. Unfortunately, I got no sleep the entire night.
The primary flaw in this system was the lack of insulation under my back. Sleeping bags are poor insulators when you lie on them in a hammock or on the ground on a thin sleeping pad. In my opinion, this is the single greatest reason why people sleep cold and blame their sleeping bags for it. I have since massively upgraded my sleeping pad to an Exped Downmat 7 for early spring & late fall trips and abandoned the use of a hammock in cooler temperatures.
A secondary flaw in my system is a little more subtle. Well ventilated shelters like hammocks and single walled tents encourage evaporative cooling. Evaporation is the process where warm water molecules turn from a liquid form into a gaseous form. For example, when you sweat, you feel cooler because the warm molecules leave the surface of your skin, leaving the cooler ones behind. So when air flows over a sleeping bag, the occupant will feel cooler because evaporation is occurring on the sleeping bag’s surface. You can validate this by getting into your sleeping bag and then sliding an emergency mylar bivy over your bag instead of inside it. You will feel warmer instantly.
While using my emergency mylar bivy as a vapor barrier worked for me in the example above, there were still other things I could have done to get warmer.
These are some tricks that you can use regardless of whether you are sleeping in a tent or hammock.
- Stuff all of your loose gear into your sleeping bag. This will reduce the volume of air that you need to keep warm using your body heat.
- Put all your remaining clothes on. In particular, your rain gear will act like a vapor barrier liner.
- Close off all shelter venting except for a small breathing hole. I could have done this by dropping my tarp lower onto the hammock top.
- Boil some water and sleep with a hot water bottle in your sleeping bag.
- Stuff leaves and forest duff under your tent footprint or between your hammock underquilt and your hammock.
- Layer non-breathable clothing between your hammock and your hammock-quilt to form a better vapor barrier.
- Fill your pack liner and all your stuff sacks with dead leaves. Arrange them underneath you in a tent or hammock as an organic sleeping pad.
- Tighten your sleeping bag around your upper chest. This helps reduce the amount of hot air that gets released when you move in your bag – called the bellows effect. This is why good cold weather sleeping bags have draft collars.
I didn’t use these tricks on my Long Trail trip but on hindsight I should have. I guess that’s the utility of experimenting with your sleep system.
If you find some of these tactics useful or have others you’d like to share, please leave me a comment below.
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