Have you even 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 not still not solve the problem. I can speak from experience!
You need to understand that your sleeping bag in 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 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 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 1000 ft. Winds were relatively calm.
My sleep system included:
- an 800 fill goose down REI Kilo sleeping bag rated for 20 degrees
- Hennessy Hammock, Ultralight Asym
- Jacks R Better tarp
- Jacks R Better Nest - an 800 fill goose down hammock under-quilt
- Capilene 3 top and bottom long underwear
- Cocoon Polarguard vest
- fleece cap
- an emergency mylar bivy
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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7 users commented in " Sleep System Tactics for Staying Warm "
Follow-up comment rss or Leave a TrackbackWell written post and some great ideas. We are lucky in Australia where most camping is in warmer climates. Our other issue in cold areas is there is often no vegetation to use as an “organic sleeping pad”
I’m packing for a trip this weekend and almost decided to leave my pack liner behind because I expect dry weather and wanted to shave the weight (1.7 oz.) I reconsidered because it will be fairly cold at night and I can use the plastic bag as a vapor barrier shirt or half bivy if I need to. I’ve done this before, in fact.
I’ve been thinking about Australian camping since your last post. I seems like you have many more nasty critters to worry about than in the states. Is that true or have I been scared by sensational TV? Is there anything you do special to prevent encounters?
Don’t forget to eat before you go to sleep - especially if its below zero (-18C) the extra fat will keep you internal furnace going.
After all, everything you mention only prevents the heat loss, except maybe hot water bottle. For me the most important part of the system is the person himself / herself and their ability to produce heat. Some of my girl friends freeze at night in their zero degree bags while I at the same time boil over in my 30+ degree bag and have to use it as a blanket.
I could have used these tips a few weeks ago! I’ll keep them in mind on my next trip.
I like the survivalist use of leaves, etc.
I like to avoid filling my sleeping bag with stuff other than the hot water bottle or the next mornings clothes, but that’s just me. When it is going to be really cold I incorporate a space blanket into my sleeping system as a ground cloth in the tent, then use a closed cell foam pad and a thermarest. I also take a flannel sheet or small fleece blanket. I will put my outerwear over the bag…no sweating or wetness inside the sleeping system. Of course if it gets really jacked up then you just wrap up in the space blanket.
I think Tom is on to something when he talks about a person’s ability to produce heat. I personally am too hot if the temp goes over 65 and this winter I left the heat off during the nights. I had three blankets - the “warm” blanket (a cheap $4 buy made out of fleece) that went next to my body, the “cool” blanket that was a simple store bought flat quilt, and a knitted afghan that went over the top. I slept in just a T-shirt, never had to wrap the blankets over my head (although I did wrap my body with the blankets) and was as comfortable as a bug in a rug. I think the lowest temp was 43ºF. Most people pop their eyes when I tell them this but I can get away with it because I know I am a “cold” person.
Downside - I’m miserable sleeping in anything over 60º.
Last year I lived in a flat in New Zealand with almost no insulation, ice inside the windows in the morning and all that jazz. I figured out pretty quickly that if you simply sleep in a fetal position you’ll always stay a lot warmer. Getting into a ball will decrease your body’s total surface area for heat loss by a large margin. Poof! instant 5-10 degrees added to your sleeping bag’s rating. (alternatively, you can just take a polar bear swim on occasion, and your body will adapt to the cold to a surprising degree. though no one ever said it was a comfortable process…)
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