How warm is this sleeping bag? What sleeping bag do I need for camping next week?
These questions and others are regularly asked in the shop and as ever the answer is not simple. You will probably noticed that sleeping bags have various temperature ratings associated with them, they are usually sewn onto the bag or printed on.
But what do they mean? All bags sold in the EU now need to be checked for warmth or thermal ability under EN 13537 which was supposed to standardise and simplify the system for sleeping bag ratings. I am not sure this was achieved given the explanation of the rating system below.
Most sleeping bags will have 3 or 4 temperatures on them these are:
- 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).
These tests are carried out in the lab using probes on a standard man or woman manequin (is anyone standard?) laid on a sleeping pad, in a tent wearing 1 layer of thermal clothing.
It might be just me, but this does not help at all when deciding which bag is right for me. You may buy a bag that quotes the extreme as -12c thinking it will be nice and warm at 0c hwne in fact you will have a miserable night.
Some manufaturers have tried to simplify this by using Comfort, Transition and Risk.
Clearly the Extreme/Risk must be ignored, who wants hypothermia when camping?
The Lower Limit/Transition is also worth ignoring as most people do not sleep in a 'curled position', again its hardly the criteria for a happy experience.
So the only ratings worth looking at are Comfort and Upper Limit. Even these are a rough guide as so much depends on other factors.
The biggest 'other' factor is what you sleep on, generally speaking any insulation underneath you is worth twice that of insulation over you. In real terms cheap infaltable airbeds offer no insulation and will make sure the user is cold all night, closed cell foam mats are little better. To insulate effectively look at Thermarest mats or Vango mats to keep the cold away, their thermal rating is far higher than anything else, they also have the added bonus of being much comfier.
Your choice of bag will also depend on your own sleeping habits, are you a warm or cold person? will you use the hood and drawcords?
To conclude our advice is to buy a Thermarest or Vango mat to sleep on and to buy a bag that is warmer than you think you need - its easier to make a bag cooler (undo the zips etc) than warmer. Ignore all the temperature ratings apart from the Comfort and Upper, Comfort will work for most men and Upper for most women.
You could be forgiven for thinking this bag would be OK at -18c when in fact you would be hospitalised with Hyperthermia and/or frostbite. This bag will, in fact, only be OK down to 3c at the lower end.