[hodgesrm]

That’s how snow caves are constructed. Tunnel in and up in a snowbank so that the floor of the cave is higher than the ceiling of the entry tunnel. The air in the cave will equalize to 32F once you enter thanks to body heat. As far as I can tell this works well in any temperate climate because the snowpack tends to be warm(er) at the bottom and warmer air rises.

At any rate it worked in all my snow caves, which was admittedly not a large sample but included places like Teton pass in Wyoming.

[throwaway2037]

> The air in the cave will equalize to 32F once you enter thanks to body heat.

This is an interesting post! Can you explain the science behind why 32F/0C is important here? For example: If I build a snow cave in a place where it is -30C, -20C, -10C, 0C outside, will they all "equalize to 32F/0C"?

[devilbunny]

Snow is a very good insulator due to all the trapped air, and it’s fairly easy to make thick walls (the same as straw-and-mud block construction - not the highest R value per cm thickness, but if the walls can be 50 cm thick, it adds up). So yeah, a proper snow cave will converge on freezing point - body heat plus lighting will heat to that point, after which the snow melts.

[huytersd]

You might survive 32F but you can’t possibly make it for very long if you have to be that cold night after night.

[hodgesrm]

Actually 32F without wind is no big deal if you have a decent sleeping bag. Plus it gets warmer as you do more stuff inside (e.g., cooking). Igloos have the same design and can get pretty warm. [0] The real problem in my experience is that it's quite humid. Since you are insulating with snow it evaporates and raises the humidity up to the dew point.

[0] https://en.wikipedia.org/wiki/Igloo

[huytersd]

I guess it varies from individual to individual. I can be out in 110F weather all day comfortably if I have enough water and a large hat but have very low tolerance for the cold.

[gen220]

Inside the sleeping bag, it will definitely be quite warm!

Even quite mediocre sleeping bags (by modern standards) are positively toasty at 32 degrees. It was common in my group for people to sleep in their underwear in the caves! Our sleeping bags were 0 degree rated, though.

[dredmorbius]

Further: the major source of heat loss in a sleeping bag isn't to the air, it's to the ground. Which is why backpackers carry sleeping mats, either of expanded polystyrene or self-inflating air-mattresses. In both cases, the air is the insulating element.

In primitive conditions, pine boughs or fur skins would be used.

Other than that, wear a cap, and if it's truly cold, boil water, pour it into a Nalgene (or similar) bottle, and slip that into a sock. It'll keep you toasty (often too warm) all night.

[worik]

> mediocre sleeping bags (by modern standards)

Sleeping bags have been very good for a long time

"modern standards" means cheaper than goose down

[gen220]

You have to poke holes in the ceiling, and make sure the they’re clear every day.

If you light a candle, the snow will melt and freeze into a film of ice.

The holes are important for ventilation in general, but it also allows vapor to escape.

When we built them we’d use ski poles to make the holes. You don’t want them to be too big or you risk the structural integrity of course. There was a ratio of hole count : people that we followed but I can’t remember that detail (: