"The "Little House" books by Laura Installs Wilder and learned a lot about all sorts of things. One thing that their family did while living in South Dakota during a long, hard Winter was that snow can act as an insulator. You can build a cave, tunnel, even an igloo (not in her books). If it is below freezing outside but you have a ton of snow and wind the snow will keep colder air and wind out and your body heat and breath will create a layer of ice for further insulation. That is what the books said and it makes sense.