A beginners guide to choosing a sleeping system for arctic use (assuming camping down to -30/-40 degrees C).
There are several schools of thought for a sleeping system for use in the extreme cold here are the main ones that I know of:
- A synthetic sleeping bag rated at around the planned usage temperature.
- A down sleeping bag rated well above the planned usage temperature.
- A down sleeping bag with a synthetic quilt or sleeping bag on top of the down bag.
- A down sleeping bag with vapor barrier layer and outer bivvy bag.
- A combination of the above.
Down vs synthetic
There’s already plenty of info on this subject on the internet so I’ll keep it short. Down = more expensive, compacter, lighter, doesn’t work so well when damp/wet. Synthetic = Cheaper, bulkier, but still insulates when damp/wet.
Background considerations for winter camping
Rather surprisingly even in winter you sweat a lot while sleeping. This sweat plus other moisture from drying items of clothing in your sleeping bag etc then builds up inside your sleeping bag/system. Condensation from your breath or cooking can also built up on the outside of your sleeping bag which could be absorbed. Usually in warmer weather this moisture just evaporates into the atmosphere, if its -30 for example the moisture freezes somewhere. That somewhere being the place in your sleeping system that is around 0 degrees C.
On a longer trip where you are outdoors most of the time you have little or no chance to dry your sleeping bag out so you need to take this into consideration. Especially when using a down sleeping bag as the insulation value will degrade as the down gets wet.
Pro’s and Con’s of the various sleeping systems :
1. A synthetic sleeping bag rated at around the planned usage temperature.
In theory the only downside of this system is the bulk and weight, a synthetic sleeping bag rated to -30 degrees C would easily take up a full rear pannier or more and probably weigh 3-4kg (I’m guessing).
2. A down sleeping bag rated well above the planned usage temperature.
It’ll be too warm the first couple of days but you can reduce that by opening the zips a little or leaving the tent door open. Then it will be fine for a day or two. This system will work for a short trip or if you can get indoors and dry the sleeping bag every few days.
3. A down sleeping bag with a synthetic quilt/sleeping bag on top of the down bag.
The theory is the evaporating moisture and the 0 degree point will be in the synthetic layer, keeping the down sleeping bag dry. This is kind of a compromise between option 1 and 2 and probably one of the most used solutions. It also means you can use a 3-4 season down sleeping bag you already have without investing in an expensive -30 rated down bag. The major consideration here is that your outside sleeping bag will have to be oversized so that it doesn’t compress the inner sleeping bag reducing its “loft” and therefore insulation. There is also the advantage that on the coldest nights you can put on a fleece or down jacket too.
4. A down sleeping bag with vapor barrier layer(VBL) and outer bivvy bag.
The down sleeping bag is your insulation layer, by sleeping inside a vapor barrier (in practice a plastic bag or similar waterproof layer) all sweat stays inside the vapor barrier and not in the down. The gore-tex bivvy on the outside stops condensation getting into the down from the outside. In theory this system means you can keep your down sleeping bag dry without taking too much extra weight with you or too much extra space in your panniers compared to a quilt/extra sleeping bag.
The biggest downside of this system is you are always a little damp, cycling/sweating all day then sleeping inside a damp vapor layer. In the long term this could cause problems with athletes foot and similar problems. It also mean you can’t dry other clothing etc inside your sleeping bag.
5. A combination of the above
I’m lead to believe for the really extreme stuff that a combination of vapor barrier layer, down bag and quilt is the best option. But as cycling at -50 is pretty much impossible I doubt I’ll ever need to find out.
For Lapland I went for option 4 and found it worked fairly well. Sleeping inside a VBL was not as bad a I thought. That said I suspect that if you have the space that option 3 is more pleasant.
About sleeping bag ratings :
Many sleeping bags in Europe are now rated according to the EN13537 Standard. Which involves a manikin test.
From Wikipedia:
EN13537 requires a thermal manikin test which produces four temperature results — upper limit, comfort, lower limit and extreme. These temperatures were worked for normal consumers.
The standard measures four temperature ratings:
- Upper Limit — the temperature at which a standard man can sleep without excessive perspiration. It is established with the hood and zippers open and with the arms outside of the bag.
- Comfort — the temperature at which a standard woman can expect to sleep comfortably in a relaxed position.
- Lower Limit — the temperature at which a standard man can sleep for eight hours in a curled position without waking.
- Extreme — the minimum temperature at which a standard woman can remain for six hours without risk of death from hypothermia(though frostbite is still possible).
For the purpose of these measurements, a “standard man” is assumed to be 25 years old, with a height of 1.73 m and a weight of 73 kg; a “standard woman” is assumed to be 25 years old, with a height of 1.60 m and a weight of 60 kg.”
Bear in mind the Manikin for these rating tests is wearing a base layer, socks, and hat.
It seems to me to be fairly flawed that one limit uses a man as the base , the other a woman, and the lower limit is a joke. Ever tried sleeping in a curled position for 8 hours in a mummy type sleeping bag?
Anyway, its just an indication but its handy to know what these ratings are based on…
