In extreme cold the outside temperature goes down to as low as -40 degree centigrade while the inside will be remaining in the range -7 to 15 degrees. So this is a type of insulated capsule in the ocean of snow in cold places.
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The insulation provided by the snow is known as Igloo effect. This insulation effect is due to the air pockets in snow crystals. They will keep the temperature from dropping below zero degrees. But the inner walls require some maintenance as the snow on the inner wall melt due to radiation and conduction of heat from the humans as well as from animals also.
Igloo effect exists only in sub-zero temperatures but not at high temperatures. The temperatures are relatively higher inside than outside. If outside it is minus 5 degrees centigrade, the temperature inside maybe around 0 degrees centigrade but can't be 10 degrees centigrade.
Igloos are made up of blocks of compressed snow. The compressed snow has air trapped in it and the air is a bad conductor of heat. Hence, the heat given off by our body does not get lost from the igloo.
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