Sleeping Systems

In a cozy hot tent, almost to retire for the night in 3 different sleeping systems. Left: one single big goose down bag; Middle: inner goose down bag and outer fiber overbag, with sleeper using inner vapour barrier; Right: inner and outer fiber bags. All sleepers wearing long underwear plus a light fleece layer. All using large over-sized bivy bags on the outside. All sleepers on inflatable sleeping pads with empty duffels and other stuff underneath for more insulation. Floor base is a bough bed (or a tarp can be used instead if snow is really packed hard). Note center sleeper with boots tucked under out of the way for efficient use of space. Note aluminum heat shield in front of stove.

You are heading out for a winter camp and the forecast is for nights of -40.   Yah!   You are so lucky!   Really, I’m serious.  I actually wish for -40 on winter camping trips, but its only on a few that it actually gets that cold.   Those nights tend to have no wind, no clouds, stunning star viewing, and the trees crack and the lake ice booms, and I mean booms!   Once you develop your sleeping “system”, you will be looking for those deep cold opportunities.   Minus 20 nights will soon seem almost balmy.  Get a few under your belt and you enter a whole new world of confidence in living and travelling well in winter.

If there is any misinformation or poor advice in the popular media about winter camping, it is often about sleeping systems.  As soon as you read articles advising you to wake up often to eat to stoke your internal furnace, or to rely on hot water bottles or other gimmicks to heat up your sleeping bag, you should be wary about this and the rest of the article.

Winter camping is hard work and you need a good nights sleep.  The last thing you should be doing is deliberately waking up to eat periodically.   You would not do that at home to stay warm, so why would you do that in the bush?    Don’t wake yourself up to eat.  Your dinner should have been a high calorie dish generous on the fat, and this is more than enough to burn away all night.   You are a human being – you are supposed to sleep 8-10 hours a night and your body is well adapted to do this.  Other than the occasional need to get up for a pee break, you should be planning to sleep deep and sound.

The hot water bottle advice thing is a stop-gap measure and if you need use it to get you through the night, then it means that your sleeping system is on the very edge of failure.  Should it get any colder, you are going to suffer unless you layer up with more clothing.   Needing a hot water bottle means your sleeping system is not warm enough.

In the “old days” winter trekkers slept in caribou hides, or they kept all their winter clothing and moccasins on and wrapped themselves in one or two wool blankets.    Nowadays, the concept of sleeping in all your clothing and boots is not in style (although maybe it needs re-examination).  We all seem to have converted to a travel style of stripping outer clothing off and using a sleeping bag to stay warm.  There are definitely advantages in sleeping comfort to the modern methods, but you do pay a price in heavier bulkier sleeping gear to haul on your sled.  I guess they were tougher in the old days!

There is no getting around the need for a high loft, high insulation sleeping bag, or combination of 2 bags which create a high loft.  High quality goose down bags are by far the optimum combination of light weight, compressible packability, high loft, and long-term durability through years of use.  Various high-end synthetic fiber fill bags will also do well, and are less expensive than goose down, but they can’t compete with down’s weight to insulation loft ratio, nor with down’s superior durability through the years.   Eventually fiber fill bags, if well used over several years, will clump, degrade and lose loft and insulation rating.  By far, down is superior in all measures, with the caveat that you must keep it dry.  Get it wet in a winter rain storm and you are in deep trouble.  If you go with down, you must keep it dry at all costs.   Other than price, the ability to dry a wet bag is the one advantage fiber fill has over down.     Personally I own and use down sleeping bags and find them the best for my camping style.

With both goose down and fiber fill bags, it is essential to keep your bag clean inside and out.  The less you have to wash the bag, the longer it will last and maintain its loft.

In this section, we will be discussing sleeping “systems” which will get you through the night in comfort, and be adaptable to a wide range of conditions.

The Big Bag

After a few beginner trips where I layered two summer weight fiber fill sleeping bags, I opted for the single big bag option to cover the deepest cold conditions.   I purchased a -40 goose down bag, generous mummy fit, with extender for lots of room.  The advantage to an ultimate deep cold bag is that I only need one bag on a trip and I have total piece of mind.   The disadvantage however is that I am usually quite hot at temperatures warmer than -15 deg. C, and have to use ventilation techniques sleeping inside a bivy bag with the bag unzipped  (see below for bivy bags).   Believe it or not, one of the challenges I have when sleeping out in winter is staying cool!   Not a bad problem to have – it beats the alternative!   On some trips this bag is overkill, and it was very expensive, but it does the job, and it will last for maybe 20 years if I keep good care of it, and I only really need the one bag for the northern areas I camp in.

Big -40, toasty warm Mountain Hardwear goose down bag, in the morning after a deep cold night, showing frost on the outside from exhaled breath around cinched hood. Make sure your breathing stays outside the bag to avoid any frost on the inside. Note the bag is inside a peeled back bivy bag (shown with breathable membrane in yellow).

Inner and Outer Bags:

An alternative to one big expensive bag is to use thinner inner and outer bags.     On warmer nights or warm trips where you are confident of the forecasts, you may need to bring only one bag.  One buddy purchased a -20 goose down bag as his base inner bag, which is often suitable alone (inside a bivy bag – see below) for early season trips.  For deep cold trips, he layers an over-bag on top of this and with the rest of his sleeping system, he is good to -40 no problem.

If choosing a two bag system, you have to be very careful that the outer bag is generously sized so that it does not compress the loft on the inner bag.     Compress the loft and you defeat the purpose of your bag layering system.   There are dedicated over-bags on the market designed to fit loosely over lofty winter bags.  Another buddy staying on the low budget plan, has selected two old fiber fill bags that he ensured were compatibly sized for layering.

On sunny dry mornings, a frosty bag will dry very quickly in the sun through the magic of sublimation. Mountain Hardwear goose down bag turned inside out. Note black inner colour on most of inside, which absorbs heat.

On a cold, dry sunny morning of -25, in minutes the sun will sublimate frost directly and/or melt and evaporate the frost off your bag. Mountain Hardwear and other high-end winter bags are made with a highly water resistant outer shell for this very reason. Water beads up and evaporates without wetting the bag’s insulation. This bag is mostly black which is the best colour for a winter sleeping bag’s inner and outer fabric, but the intense sun will work on lighter colours too.


The advantages to a 2-bag system is versatility, and a lighter smaller load for warmer weather trips.   The disadvantages with a 2-bag system is a bulkier packable volume when bringing both bags, and potentially heavier weight than a dedicated single bag.

Both single and double bag systems work well, but DON’T cheap out on your sleeping bag system.  Make sure you have enough insulation function to extend into colder than anticipated temperatures.

Bivy Bag

I and my buddies use waterproof and breathable, over-sized bivy bags over top of our sleeping bag systems.   The big, baggy bivy bag serves many functions.  First, it protects the bag from contact with snow which, if it gets under your bag, will melt and wet the bag (and that’s very bad!)   Secondly a bivy bag will protect your bag from dirt, sharp branches and needles, and spruce and balsam gum.   You need to keep an expensive, lofty winter bag very clean because you want to wash it as little as possible in order to maintain its original loft.

 Integral Designs’ super roomy Bugaboo model bivy bag with breathable membrane. Huge size made to fit over the largest of bags without crushing the all important loft, such as this lofty Mountain Hardware -40 goose down bag. Bivy adds a tad extra warmth, helps with moisture transport out of the bag, and protects the bag from snow, dirt and debris. Sleeping pad is the thick cushy Thermarest LE.

: In the morning showing the inside an Intergral Designs Bugaboo bivy bag with frost on the inside of the waterproof bottom. Breathable membrane on top and sides in bright yellow has some frost, but some was also transported out. This frost would have crystallized inside the sleeping bag, but the bivy keeps a bubble of warm air just enough to let some moisture fully out of the down bag, keeping it drier. In the morning, simply turn bivy bag inside out and shake out the frost.

Thirdly, if the bivy bag is generously sized to be lose fitting, it will trap a bubble of warm air which will allow a significant amount of the moisture generated in the bag to escape the outer zone of the bag before it crystallizes into frost.   When cold camping for extended periods, frost builds up in the bag from condensing moisture, and this will reduce the insulation ability and add weight to the bag.   But by using the bivy, much of this moisture frosts up on the inside of the bivy bag, outside your sleeping bag.  In the morning, simply pull out the sleeping bag, turn the bivy bag inside out, and shake the frost out of it.    The “breathable” function is limited once the frost plugs the membrane, but I am convinced that some of it does escape the membrane through sublimation pushed by the heat differential.

Fourthly, for those of use who use a -40 one-bag system, you can vent excess heat on warm nights by unzipping the bag inside the bivy bag.   On nights warmer than -20 deg C, I sleep with the sleeping bag mostly unzipped since otherwise I am too hot.   The bivy seems to let the heat out of the open bag at a comfortable rate, and there is also the bonus that lots of moisture is leaving the unzipped bag and venting out into the bivy and then outside.

Vapour Barriers

There are two types of people in this world…..

Vapour barriers are inside bag liners of plastic which completely trap all moisture emanating from your body.   The theory is that once your body is saturated with a base load of moisture, your body will stop perspiring, and the moisture does not escape into the insulating material of the bag.  Therefore no frost gets into the bag.  Proponents of vapour barriers also report a 5-10 degree C extension of the temperature rating of their system.

I have never tried a vapour barrier system.  There is something about sleeping inside a plastic bag which is not appealing to me.  However there is no denying the satisfaction of vapour barrier users, and if you are doing an extensive cold camping trip, you will need to rid your bag of frost.   Late in the season you may have long sunny days where you can place your bag in the sun and the frost will sublimate out of your bag almost like magic.  But early in the season, you may be packing and unpacking your bag in the dark without the benefit of sunlight to dry it, and a vapour barrier is one solution to the problem of drying out your bag.    For long expeditions using cold camping style, where time off to dry out a bag is not possible you may have no choice but to use a vapour barrier.    Hot tenters of course don’t have the problem of drying out a bag if they make the time inside to dry their bags morning and evening.   And if you are old school and use wool blankets or caribou hides, you have the last laugh at the high tech crowd, since you can simply beat your blankets or hides with a stick and the frost will fall out.

Sleeping Pads:

Much of the heat lost in your sleeping system will be through the ground and snow underneath you.  In fact when sleeping directly on the snow with only a ground sheet underneath, you will literally melt your way into the snow, and be quite cold as well, regardless of how lofty your bag is.   You need an airy insulative pad underneath you to stay warm and dry in winter.

In the old days, they used thick beds of black spruce and balsam boughs layered like shingles, and this is still the traditional method of choice for modern winter campers where regulations allow, (i.e. not in Parks which tend to have no cutting of live vegetation rules).    Recall that winter campsites are tucked into the thick bush, not near any summer open breezy campsites.  Up in the Boreal, the forest is burning and blowing down all the time, and dominated by tens of millions of hectares of conifer forest, so a relatively few winter campers spread out over vast landscapes and through time, snapping off a few armfuls of spruce and balsam is not a conservation issue.   In heavily used landscapes further south, it could be a conservation issue, so your landscape context is very important.  In Canada, we are extremely lucky to have vast areas of Crown (publicly owned) Land, and using traditional bough bed techniques is possible in many areas if done with a conservation ethic, and respect for the trees and for fellow trekkers to come.   Techniques like taking a few branch tips from many trees, and only taller trees which have lots of upper branches in the sun, is one kind of ethical practice which does not hurt these trees.   However conifer trees will not regenerate snapped lower branches, so keep this in mind.

Regardless of whether or not you can use a bough bed, you will need a sleeping pad under your sleeping bag.   Higher loft self inflatable pads such as Thermarest LE pads are an excellent choice.   Let them self inflate and avoid as much as possible blowing them up because you are blowing in moist air that will freeze.   Personally I prefer a lofty self inflating pad partially inflated so my tail bone area will sink down and the sacral area will be supported – otherwise I suffer back pain.  Without a bough bed, I would have to use a waterproof ground sheet on the snow, and if really cold, I would add a closed cell foam pad under the inflated pad.    Rolling up or flattening out a closed cell foam pad at -30 to -40 is tough.   A pre-creased pad like a Thermarest Z-Rest is an excellent choice to avoid the perma-curl foam pad effect.

Sleeping Clothes 

Despite the fact that I use a -40 goose down bag plus bivy bag overtop, I still need sleeping clothes.    Obviously the thinner the bag, the more sleeping clothes one needs.   This section will discuss sleeping clothes body layers and head/face wear separately.

Sleeping body wear I don’t follow nor recommend the advice that is commonly found in the popular winter camping literature where they promote the concept of changing from your day inner layers (long underwear, socks, base fleece), into a dry set of sleeping clothes.   This means getting naked and changing before bed and worst of all, when you get up in the morning which is often the coldest part of the day or night.  I think it’s crazy to strip naked in the morning to then get into freezing cold day clothes.   Try doing that at -40 in the morning just once, and you won’t try that again.  Furthermore, those so-called dry sleeping clothes on morning one will now have a base load of moisture, and will even be wetter if you used a vapour barrier bag, and so where’s the next dry sleeping clothing layer supposed to come from?

I and my buddies simply sleep in our inner body layers that we had on during the day, because we dried them by wearing them in the evening.   In the morning, we pop out of bed and quickly in the deep cold and get our outer layers on, and just that effort will warm you up.   The socks you are wearing in bed are warm and dry and they bring a base load of heat into your frozen boots.

If your inner layers are wet with sweat or frost just before bed, then you are doing something wrong.   Setting up camp will generate a lot of heat and moisture and you may get partially wet with sweat.  But after camp is set up, the evening is for calming down and drying off the inner layers simply by spending time by the open fire or in the hot tent.   Your inner heat pump will pump that moisture into your outer layers, and the fire will evaporate/sublimate it away from the outer layers.  (See our Clothing section for discussion on inner wicking layers, and fire-friendly outer layer fabrics).

Drying socks in a hot tent is fairly easy, but very difficult when cold camping.  It’s easier just to dry them by wearing them.    Felt boot liners are very efficient in absorbing moisture from your socks, and amazingly I find my socks almost dry at the end of the day even when the boot liner is soaking wet and frosted inside the boot.   I bring a second pair of boot liners and alternate the boot liners, drying the liners, not my socks.

With a big single -40 bag, I typically sleep in my expedition weight polyester long johns base layer, and sometimes my first light fleece (e.g. Polartec 100 weight), layer sweater.   On my feet I have my inner liner socks and one or two of my midweight socks.   Often my feet get too hot in the big bag, (a nice problem to have), so I strip off the outer heavy wool socks and just leave in the bottom of the bag so they are nice and hot and dry to put back on in the morning.   I change underwear for hygienic purposes, but otherwise I wear the same base layers during day and night.   For the underwear change, wait for the hot tent to be heated up, or get the cold camp fire roaring, and change in the heat.

Should your base long underwear layer not be sufficient for sleeping, layer up with dry fleece/wool from your inner insulation layers.    You can add 10-20 degrees of comfort to a thinner bag by adding sleeping layers of dry fleece or wool.

Sleeping Head Wear  This is the one set of sleeping clothing where I and my buddies do in fact reserve a dedicated dry and clean sleeping balaclava and toque that only gets used for sleeping.    First, its important to have clean headwear so that dirt and oils from your day head wear does not get into the sleeping bag hood.  Second, your day head gear is likely too bulky and uncomfortable to wear in bed – mine is anyways.  Third, your day head wear may still be wet with frost or melting snow which was falling that evening.  So you need dry headwear for bed.

I and my buddies use thin, loose fitting polyester open face balaclavas and overtop a loose fitting thin fleece toque.  This set up, ensconced in the massive hood of a winter bag keeps our noggins and face nice and warm.  I don’t like to have to breathe through any covering on my mouth and nose because it will frost up and be clammy.   My mouth uncovered is fine, but my exposed nose can get very uncomfortable beyond -20.   I bring a fleece ear band and wear it around my neck when retiring.   Should I wake up with a cold nose, I bring the ear band up over the tip of my nose, making sure that breath can escape underneath so as not to frost it up.   It works great.  If cold camping, hang the gear up (preferably in the sun) for a while before packing up and through sublimation will dry out.  Try and arrange it on your face so it does not get frosted up.  If you breathe through any face covering (which I can’t stand), it will be a mess of frost in the morning requiring more time for drying, so I avoid that problem.  A runny nose during the night is also an irritation, so have your bandana by your side for a nose wipe.

The Canadian Army used to have a standard issue winter bag system without a mummy hood, but using an independent sleeping hood covering your head and upper shoulders, and these were available through army surplus.   This is a superior technology since it allows you to thrash around independently of a hood.  Us mummy bag hood users who are also thrashers, are constrained by the hood, which cuts into comfortable sleep time.   Exhaled breath from a mummy bag hood user inevitably frosts up on the hood edges, requiring extra drying time, whereas the independent sleeping hood users can twist and thrash in any direction and exhale away from the bag.    On warm nights I sleep on top of the mummy hood and it’s such a relief to not be constrained by it.  If you find one of these army surplus sleeping hoods, snag it or let your buddies know – heck let me know!.   Hopefully one day a gear manufacturer may design and sell a similar product (goose down would be perfect for loft and compressed packability), or perhaps you could make one yourself.    Send us some pics if you do.