Outdoor stores here carry aluminized (mylar) plastic sheets which reflect heat ( = infrared).
We call them "space blankets!". About a 4" square x 1/4" thick (30g?). Not about to open one to see the area.
Have 2 of them in my (bird) shooting vest and 2 more in my day pack.
In anybody's emergency, I can imagine them getting ripped and punctured.
Condensation could be an issue but in a howling mountain blizzard, there are bigger concerns.
You aren't going to be given any chance of a nice cozy camp fire.
Two sheets to get out of the wind. Third to get off the snow, the fourth to wrap a person in.