The idea of taking shelter in a structure made from snow and ice sounds...brrrrrr. So how does an igloo keep you warm? Well, it turns out that it all depends on the type of snow that you choose to build your igloo with and the shape that you construct. Most igloos are built in a catenary arch, with various levels inside, allowing cold air to sink and hot air to rise to the uppermost level, where you would eat and sleep. Where the that hot air come from? You! You act as a living furnace to heat up the space! Let's explore more.
Another important fact of igloo architecture to take into consideration is the way cold works, or more precisely, the way heat works. When you feel cold, it's not because cold is actually entering your body, it's because heat is leaving your body. Heat can leave your body through convection, conduction, and radiation; similarly, heat works the same way in an igloo. Imagine yourself sitting in an igloo, giving off heat (radiation), that heat bouncing around in the space in the igloo (convection), and eventually leaving through the walls (conduction). The key to an igloo is minimizing the heat the moves through the walls, and you can do that by choosing to build your igloo with tightly packed ground snow. This kind of snow is thick enough to hold up against the elements, but also contains enough air to act as insulation.
So how did we humans figure our these snow architecture dynamics? By looking at nature, of course! Many animals build snow dens or snow burrows and even plants will "hide" under snow to survive the elements.