Vrftsjtryk

I spent one night outside, at -28 degrees F, in an -40 arctic bag. I had no tent, only a small poly tarp between the snow and my bag. I stayed fully clothed but barely slept due to being so cold all night.

Would a tent have kept me warmer?

The tent will definitely be warmer because it keeps the wind away. As you are sleeping your body produces heat and a tent helps keep that warmer air around instead of it blowing away in the wind.

With that said, tents don't provide a huge amount of insulation, and so perhaps a better sleeping bag is needed.

Yes, a tent would have kept you warmer

• Tents block the wind and thus will eliminate wind-chill.


• While isolation of a tent is not good it will still allow your escaping body head to be trapped inside the tent and raise it's temperature by a couple of degrees. This will already make quite a difference.

The biggest difference, however, is that you should have used a proper, isolated sleeping pad. You mentioned that there was only a tarp between you and the snow: this means that your sleeping bag was compressed where your body weight was pressing on it and you had almost direct contact with the snow. You need a good isolated pad to combat this, there is no sleeping bag in the world warm enough to prevent that kind of energy loss in direct contact to the ground/snow.

That being said, please note that your sleeping bag rating is to be taken with a grain of salt, especially the lower end 'extreme' range: after all, what does 'extreme' mean? You barely survive but with arms and legs frozen off?

See also this question on How are sleeping bag temperature ratings determined?

Assuming you have a men's bag, the -40F rating is probably the limit rating, but it might be the extreme rating. If it is the extreme rating then sleeping in -28F, it does not surprise me that you were cold. Even if it is the limit rating, you could still be cold if you did not have the proper pad on the ground, if it was windy, or most importantly are a below average sleeper in terms of warmth. At those temperatures even a slight difference in basal metabolic rate can result in feeling cold.

You should also consider what you wear in the bag. Additional clothing can compress the bag and therefore decrease warmth. The bag also needs to fit you well. If it is too big or too small, it will be colder. There is also the issue of moisture. If you cloths are wet this can decrease the insulation of the bag. You may want to use a vapor barrier at those temperatures. You do not want to breath into the bag.

Coupling all of those things, a tent will provide some warmth, but if you were uncomfortably cold at-28F, it is not going to make you comfortable at -40F.