Why doesn't an igloo melt inside?

The snowflakes falling outside of the igloo, in the harsh Alaskan winter, quickly melt when they land on its roof, and provide a replacement layer of insulation for the igloo. The ongoing freezing and re-freezing of the igloo, hardens it, and transforms the blocks of snow the Eskimos used in the construction process into a solid, icy, domed refuge. The igloo can now withstand the weight of a massive polar bear, should one happen along and have the urge to play "king of the mountain."