It is no surprise that I enjoy the cold, and so it is no surprise that I’ve spent a lot of time in some cold places.  I’ve learned a lot of things about how to sleep comfortably in the cold.  Here is what I do.

Prepared for a cold night in the Andes

Prepared for a cold night in the Andes

I take a good look at the historical temperature and weather data.  This helps me to select equipment.  The first piece of equipment most of us think about for our sleep system is the sleeping bag.

Sleeping Bag

One of the rules of thumb I hear often is to use a sleeping bag rated to 10F degrees lower than the coldest temperature you expect to see.  Personally, I find this is pretty bad advice for three reasons.

First, on a longer trip, there are going to be warm days and cold days.  There is nothing worse than sweating all night in a bag because unzipping the bag leaves you too chilled, but the bag is too heavy for the temperatures you are seeing that night.  This is very easy to experience in sub zero temperatures.  A bag rated for –40F is going to feel really warm in -20F conditions, but –20F is really cold if you aren’t wrapped up in that sleeping bag.

Second, there is no reason not to utilize the insulation you are packing for the day.  Those layers of clothes are effective insulation during the day and at night.  In addition, I’m not a fan of stripping down out of my layers in sub-zero temperatures and getting dressed again in the morning.  It just isn’t comfortable and can be pretty dangerous to expose yourself to serious cold.  Sleeping in my clothes is standard.

Finally, there are a few other things you can use to increase your insulation when the temperatures plunge lower.  First, I’ll throw my belay jacket over the top of my sleeping bag.  I’ll wear a balaclava to sleep. A sleeping pad and proper shelter from the wind can help dramatically as well.  A sturdy water bottle filled with hot water can also help warm things up in the bag.  Use this method with caution as a leak could be disastrous.

This is why I usually select a bag that is rated to temperatures 10 to 20F above the temperatures I’m expecting.  I like a –20F bag for anything down to –40F or so.  Similarly, a 20F bag is just fine down to 0F.  By taking a bag rated that way, I get some weight savings, which is always important.

An important point to keep in mind is to never pull your face inside your sleeping bag.  You exhale large quantities of moisture which will penetrate the insulation in your bag and cause cold spots and problems.  Don’t do it.

Sleeping Pad

The ground is generally a far better conductor of heat than the air.  It is vitally important to have good insulation between your body and the ground.  Your sleeping bag isn’t enough, because your body compresses the bag where you lay on it, and prevents it from holding nice warm air in the insulation.

I have used foam pads as my sleeping pads extensively.  I’ll still use foam in very warm weather.  Closed cell foam is a great pad material.  I strongly recommend carrying at least a small square to sit on in the winter.  This could be the back pad/frame of a daypack or summit pack.

There are now much better choices for extreme cold weather.  Various inflatable pads offer much better protection from cold ground.  Just like your fluffy down sleeping bag holds warm air close to you, an inflatable pad holds warm air close to you.  These can be insulated with synthetic materials, foam, or down.

My long time favorite is the Thermarest pad.  I have one that is about 15 years old, and it still works great.  I’ve upgraded to a down filled air mat, in hopes that the greater ground insulation allows me to push my sleep system to even colder temperatures.

Shelter

A good shelter is a necessity to protect from the wind and any snow / ice getting blown around.  I’ll sleep under the stars in hot weather, but in extreme cold, the consequences of not having shelter are substantially more severe.  I’ve used a variety of shelters, from tarps, to snow caves, to tents.  They are all good options and I’ll continue to use all of those options.  However, I do have a preference for tents for a few reasons.

Snow shelters are slow to build.  They take a lot of time, and can be difficult in certain snow conditions.  This takes a lot of time each day if you are moving from camp to camp.  However, they are warm and really weatherproof.  You can get away with a much lighter sleeping bag if you use good snow shelters.  They are a great option for base-camps.

Tarps are fast and light, but don’t protect like a tent or snow shelter.  They can be used to make faster snow shelters, like a trench shelter with the tarp over the top.  I like tarps quite a bit because of this versatility and light weight.  However, in general, a tarp will offer the least protection from brutal wind and wind driven snow that is often seen at altitude.

Tents are more weatherproof than tarps, and faster than snow shelters.  They are the middle ground.  I prefer a very light and simple single wall tent for the bulk of cold weather situations.  I prefer to size the tent as small as possible so that my body heat is able to warm the interior quite a bit.  The key is to have lots of guy line available.  This allows you to anchor the tent securely even in harsh conditions.

A very light tarp is handy to have even with a tent or snow shelter because it allows you to have a protected kitchen / dining area.  Cutting the wind not only keeps you warmer, but can help increase the efficiency of your cooking system.  The weight of the tarp can easily pay for itself with a decreased fuel load.  You can also hang clothes to dry under a tarp, allowing them to get lots of good airflow, but not get hit with falling snow.

Clothing

When I was a child, I heard that in the winter, it was best to sleep naked or in underwear only.  I’m not sure how or why that rumor developed, but it is ridiculous.  I wear clothes to sleep.  In extreme cold, it isn’t very pleasant to wake up in the morning and put on cold, frozen-stiff clothes.  That means I keep my clothes in my sleeping bag at night anyway.  So, rather than wasting that insulation value by padding the foot of my sleeping bag, I keep the clothes on and wear them to sleep.  The key is not to overstuff my sleeping bag though.  This means I don’t wear my belay jacket into the sleeping bag because it is too big and the insulation ends up compressed.  Instead, I drape it over the top of my sleeping bag, over the chest area to add a bit more insulation where it matters.

I have an old habit of putting any wind shell layers between my sleeping bag and sleeping pad.  In the past, before I had a thick, high insulating value sleeping pad and a sleeping bag with a waterproof breathable shell, I’d often find frost between my bag and pad.  I’d put my shell between my sleeping bag and sleeping pad to prevent the possibility of them freezing together during the night.  I haven’t experienced the frost issues anymore, but I still often tuck my wind shells under my sleeping bag to keep them warm.

Finally, the same clothing practices that keep you warm on the move will keep you warm in your sleeping bag.  A nice dry pair of thick socks works wonders for keeping the feet comfortable.  I’ll usually have my wool hat and my balaclava tucked in the hood of my sleeping bag.  If I get cold, particularly as the night goes on and gets colder, I can layer my hats to hold in the heat, and the balaclava prevents the temptation to bury my face in the sleeping bag and ruin the down insulation.

Some things I haven’t tried but have seen others use to good effect are insulated booties.  Several brands make these, and they are basically down or synthetic insulated booties that are worn into the sleeping bag and inside the tent.  I haven’t really felt the need, as I don’t seem to get cold feet.  But it is something to keep in mind.

Miscellaneous

One of the key things I’ve noticed over the years is the difference between being warm and feeling warm.  Using this system, I am warm and safe.  The first few nights in extreme cold, especially if I’ve just come from a very hot climate, can really be rough.  I feel cold.  But I’m just fine, I am warm and safe.  I simply need to acclimate to the cold, the same way I need to acclimate to altitude.  That is a key point to remember.

Wrap-up

So, what does my extreme cold weather sleep kit look like now?

Bibler Eldorado tent (see my review here)

Exped Downmat 9 (see my review here)

Marmot Col EQ –20F sleeping bag (see my review here)

Patagonia DAS Parka

Patagonia Micro Puff pants

Outdoor Research balaclava

Wool hat

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