Why do igloos heat up and not melt?

Surely they have already talked about this topic before, but you probably do not remember it. In fact, it is one of the points that are usually treated in the Natural Sciences classes of our adolescent stage, and, although it is very curious to know why, at those ages we seem to be more aware of other things. * Why do igloos heat up and not melt?*

The igloos are the houses that have traditionally been associated with the tribes of Inuit who have survived for centuries in the harsh conditions of the north pole. With these constructions they managed to have a place where the cold, especially at night, was not mortal. A priori, being fully formed by layers of ice, we tend to think that the igloos will be almost like a cold room. But, as science has shown, the opposite is true.

And is that, if there is a good insulator in the world, that is the snow. It turns out that by applying a dense layer of this icy water, you can not let the cold go out or get out into the heat, so a stable temperature is maintained, which in that remote place on the planet will always be better than being outdoors. In addition, because there are people inside the igloo, the snow prevents human heat or that of a lamp that is generated inside from being lost in the environment.

At the time it was discovered that the Eskimos also used to coat the interior walls of the igloo with skins to further reduce this loss of heat. Of course, you should not spread the belief that igloos generate heat, in this case heat is generated by people and artifacts such as stoves or lamps that are placed inside. In fact, some experts mention that you can get a heat difference between the inside and outside of 20 to 40 degrees Celsius.

And why do not they melt with that heat? The heat that is generated inside the igloo can melt some inner layer of the wall, but the blocks will not melt completely because the other layers are still cold, causing the layers that follow the melt to freeze immediately.