Sleep System Survival Tactics for Staying Warm

Camping in Winter

Camping in Winter

Have you even spent a cold night in your sleeping bagĀ  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 1,000 ft. Winds were relatively calm.

My sleep system included:

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.

  1. 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.
  2. Put all your remaining clothes on. In particular, your rain gear will act like a vapor barrier liner.
  3. 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.
  4. Boil some water and sleep with a hot water bottle in your sleeping bag.
  5. Stuff leaves and forest duff under your tent footprint or between your hammock underquilt and your hammock.
  6. Layer non-breathable clothing between your hammock and your hammock-quilt to form a better vapor barrier.
  7. 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.
  8. 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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13 Responses to Sleep System Survival Tactics for Staying Warm

  1. frank_in_oz March 19, 2008 at 6:04 pm #

    Well 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"

  2. earlylite March 19, 2008 at 6:56 pm #

    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?

  3. Tom May 14, 2008 at 9:08 am #

    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.

  4. Jason Collin June 5, 2008 at 1:58 am #

    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.

  5. juantwan July 13, 2008 at 8:08 pm #

    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.

  6. Kelly July 30, 2008 at 11:16 pm #

    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.

  7. Stefan July 31, 2008 at 8:52 pm #

    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…)

  8. The Pilgrim January 18, 2009 at 2:53 pm #

    Good post, lots of helpful hints. Another good thing to do other than eating before you climb into your bag is some quick calisthenics or pushups. Helps warm you up a bit. It's easier to stay warm after this once you get into your bag, but more difficult to get warm once your already cold.

    ~The Pilgrim.

  9. Dave September 1, 2009 at 7:40 pm #

    Folks please do not bundle up and get into your bag. Sweat will soak your clothes and should weather/conditions require you to move out…risk of hypothermia is high. Getting damp should be avoided at all costs. If you are in danger of exposure, than of course bundle up to increase your body temp and move around (either improve shelter, build fire, or beat feet out of there)

    Otherwise info is good. My routine is to strip down to thermal underwear. Block the heat loss from beneath (sleep pad), head (fleece cap), feet (fresh dry socks). Climb into sack.

    If your body cannot warm the air pocket in the bag, the advice of stuffing articles in the bag is good. If that fails…cuddle your buddy.

    • port January 29, 2012 at 6:39 pm #

      to much clothes bundled into a sleeping bag might stretch the bag limiting the effective of the bags insulating material

  10. Pony September 26, 2010 at 8:11 pm #

    Underwear is the key… Many years ago, I learned a big secret about staying warm at night. Certainly you have to be aware of heat loss through the sleeping surface itself (like sleeping on a rock.. (bad move) But one of the biggest secrets is to have a good fresh layer of clothes next to your skin. You may have been walking all day in the latest survival rated underclothes, and add an extra hundred layers of the latests synthetics to insulate you, but that will not help at all, unless you change your underclothes before bedding down. Sure, you have to spend some time during the day in washing or at least ensuring that you have a set of clean underclothes, and it’s really tough to strip down in the cold before you go to sleep, but it DOES make a BIG difference.. Once you have clean underclothes, then you can put the other layers back on and they will insulate you. Without that step, the salt and sweat that is next to your skin will cause you to wake up as an ice cube.

  11. Sam November 7, 2010 at 10:32 am #

    Good advice here, but i worry about getting youself covered in sweat with a vapor barrier!

    I slept last night in 2 degree c with windchill off a coast (half decent two walled tent). It took a while but i got it right eventually. My system was:

    Pillow for head (essential imho)

    Dressing gown on torso

    Fuzzy socks

    Unrated indoor sleeping bag.

    I was a bit cold a few times during the night but each time i managed to fill fix it by breathing into my sleeping bag – heating it up.

    Had some dreams so i must have slept well.

  12. Michael August 31, 2011 at 1:32 am #

    "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?"

    Mate, the critters exist, but you probably won't see them. In all my walking in Australia, I have seen 3 snakes (one was dead), and a mouse spider that was timid as they get. These critters exist because they are mostly timid and have senses way better than ours. They get out of the way before we see them. Of course, they are risky if you actually get bitten, but it is very rare.

    I'll take my chances with a local tiger or red-bellied black snake over a grizzly any day. :)

    Cheers from Australia!

    Michael

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