People are often surprised at just how well snow insulates against the cold. Part of the reason for the amazement is that snow is a form of frozen water. It is mostly the fact that it is water and how it lays that lends itself to the phenomenal insulating properties.
One of the properties of water is that it absorbs heat easily. In a paper container, water is so good at absorbing heat that it can be brought to a boil over an open flame without the paper burning. This is because paper isn’t as efficient at absorbing heat as the water is, so as the paper gets heated, the water “robs” the heat from the paper.
One of the main reasons water absorbs heat is because it transfers it readily to other water molecules. Put in another way, heat flows from the warmest areas to the coldest areas. Water is amazingly efficient at transferring the heat, more so than can be said of most other naturally occurring substances.
As the water freezes into snow, it forms a six-point lattice that still has the heat retaining properties of water. It also cushions against other snow flakes, with gaps of air between them. The air pockets add to the insulating properties, much in the way that clothing does, due to the air pockets. Even as snow melts, it retains pockets of air until the snow turns back into liquid water. The air is also held close to the freezing temperature of water, even when the outside air temperature is far below that.
The crystalline structure of snow makes it highly reflective. Energy is reflected in all directions. Other snowflakes then reflect the energy again. This is the reason snow appears white and why it can be blindingly bright when sunlight shines on the snow. Light isn’t the only form of energy that is reflected, however. Heat is also bounced in all directions, including toward the source. This has a similar result as putting a shiny piece of metal or a mirror behind a heat source, to force the heat outward.
The reflective ability can even be stronger than the property of absorbing heat. What is more, heat causes the snow to warm up just enough to partly melt before it refreezes. This creates a compacted form of snow, which is even more reflective than regular snow flakes.
All of this combines to make snow a phenomenal insulator. It is no mistake that survivalists often make snow caves, in order to keep warm and to prevent themselves from freezing to death when caught in heavy snow. In fact, as related by Buzz T. who made snow caves for fun when he was less than 12 years of age, “Once the cave was built, a single candle created a lot of warmth. I once built a snow cave when the outside temperatures were hovering just above zero [F.]. Within a half hour, it was about 50 degrees in the cave, and the interior walls were glassy from the snow that had melted and froze again.”
Another man, Mr. Adams, lived many years in a mountainous national park that got large quantities of snow. He loved it when there were at least several feet of snow on the ground. “The higher the snow got, the lower our heating costs were,” he once said.
Snow has surprising insulating properties, though the reasons aren’t hard to figure out. As with most insulators, too, the more there is, the better it insulates.