An igloo, also known as a snow house or snow hut, is a type of shelter built of snow, typically built when the snow can be easily compacted.

Although igloos are stereotypically associated with all Inuit, they were traditionally associated with people of Canada's Central Arctic and Greenland's Thule area. Other Inuit people tended to use snow to insulate their houses, which were constructed from whalebone and hides. Snow is used because the air pockets trapped in it make it an insulator. On the outside, temperatures may be as low as −45 °C (−49 °F), but on the inside the temperature may range from −7 °C (19 °F) to 16 °C (61 °F) when warmed by body heat alone.

The snow used to build an igloo must have enough structural strength to be cut and stacked appropriately. The best snow to use for this purpose is snow which has been blown by wind, which can serve to compact and interlock the ice crystals. The hole left in the snow where the blocks are cut is usually used as the lower half of the shelter. Sometimes, a short tunnel is constructed at the entrance to reduce wind and heat loss when the door is opened. Snow's effective insulating properties enable the inside of the igloo to remain relatively warm. In some cases, a single block of clear ice is inserted to allow light into the igloo. Animal skins were used as door flaps to keep warm air in. Igloos used as winter shelters had beds made of ice and caribou furs. These 'ice beds' are unique to the region and Inuit culture.

Architecturally, the igloo is unique in that it is a dome that can be raised out of independent blocks leaning on each other and polished to fit without an additional supporting structure during construction. An igloo that is built correctly will support the weight of a person standing on the roof. In the traditional Inuit igloo the heat from the kudlik (qulliq, stone lamp) causes the interior to melt slightly. This melting and refreezing builds up a layer of ice that contributes to the strength of the igloo.

Source: Igloo from Wikipedia

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