Igloos prevent the warmth of the body from getting lost to the outside air. The blocks of snow used to build the igloo contain a large amount of trapped air. Fresh snow has a density of only 8 percent water; even when tightly packed it only reaches 30 percent. It is therefore the air trapped in the mesh that provides the heat insulation properties. This makes snow an excellent insulator, far better than the ground.
A well-built igloo is strong enough to support the weight of a man standing on the top of its dome. An experienced person can build an igloo in about an hour. A battery-powered lamp inside the igloo can add additional strength. The heat from the lamp causes the snow on the walls to begin to thaw. The water quickly re-freezes, producing a layer of ice.
Even when the temperature outside is as low as minus 50 degrees Fahrenheit, inside an igloo it can reach around 60 degrees Fahrenheit from body heat alone. But the temperature can be as low as 20 degrees in the corners near the ground.
