How An Igloo Keeps You Warm

An igloo is constructed using blocks of snow, and snow contains numerous tiny air pockets. These air pockets act as excellent insulators because air is a poor conductor of heat. As a result, the heat inside the igloo does not escape easily, and the interior of the igloo stays much warmer than the outside cold conditions. The dome shape of an igloo evenly distributes the heat inside, preventing the formation of cold spots and the interior of the igloo stays much warmer than the outside cold conditions.

[crazymangames]

Its also the reason you can dig a hole in a snow bank and stay warm in an emergency.

[IwantMastery]

The guy who was making that ice igloo: Forestpath (correct me if im wrong)