Build a fire inside an igloo, and the inner walls will slightly melt, then refreeze into a smooth ice layer. This thin layer seals gaps and boosts insulation, helping the shelter remain surprisingly warm even when outside temperatures plummet well below freezing. Igloos work because compacted snow is a natural insulator. Snow traps air within its crystalline structure, … [Read more...] about How Igloos Keep You Warm in Extreme Cold