How an igloo stays warm at minus 40

Snow is mostly air

Snow is a loose lattice of ice crystals with air trapped between them. Fresh snow can be up to 90% air, and air conducts heat very badly, so a wall of snow works like a thick duvet. Builders need snow packed firm enough to cut into blocks, but even wind-packed snow is still mostly air.

The shape does the heavy lifting

Traditional igloos are built as a catenary dome, the same curve a hanging chain makes, turned upside down and spun around. That shape keeps every block in compression with no bending forces, so the structure gets stronger as the snow settles and the blocks fuse together.

Heat rises, so the bed does too

Builders dig the entrance tunnel below floor level and raise the sleeping platform. Cold air sinks into the tunnel and warm air collects where people sleep. A small vent at the top lets stale air escape, so the air inside stays fresh.

With body heat alone, the inside of an igloo can stay between about -7°C and +16°C, even when it is -45°C outside.

A lesson for web design?

Good structure first, decoration second. It is the same principle behind every Igloo theme block: get the bones right and the rest is easy.