Igloos keep residents warm through a variety of different construction elements, including the combined use of compact snow in the main blocks and ice along the interior walls. Additionally, the manner in which the interior is terraced adds efficiency to heat retention, as does the angular considerations of its exterior design and points of ingress and egress.
Igloos are not built primarily from ice blocks, but from blocks of compressed snow. Not only is compressed snow lighter than ice, it is a superior insulator, possessing multitudes of air pockets. While the exterior of the blocks remain as such, the interior face of the blocks is commonly melted due to warmth generated in the interior, creating a sheet of ice that further shields and preserves the heat inside.
Igloos also do not have singular flat bottoms. Instead, the feature of terracing allows an upper portion for habitation, a middle portion for fire-building and a lower portion for the escape of the coldest air, a feature referred to as a cold sump. Consequently, all the warmest air rises into the portion where people live.
The entrance to the igloo is traditionally built at the bottom, another feature that protects the activity of the cold sump and prevents the escape of heat. Construction of igloos usually contains at least one right angle, an element that fends off large gusts of wind that might otherwise enter the structure, chill its inhabitants and snuff out the fire. The simple design of the interior maximizes the heat produced by people's actual bodies, similarly to the way a common blanket functions, by securing body heat.