An igloo seems like it shouldn’t work. It’s made of snow blocks, sitting on snow, in subzero Arctic weather. Yet stepping inside one, you find it’s remarkably warm - sometimes 50-60°F warmer than the outside air. With a small lamp burning and a few people inside, an igloo can be cozy enough that you’d want to take off your jacket.
The trick is snow’s insulating power. Fresh snow is full of tiny air pockets, and trapped air is one of nature’s best insulators - that’s the same principle behind down jackets, sweaters, and double-paned windows. The blocks of compacted snow used in an igloo trap air similarly, dramatically slowing the loss of heat from inside to outside.
Once the people inside settle in, their body heat alone (plus maybe a small oil lamp) warms the interior. An igloo also has a clever shape: the entrance is below the main floor, so cold air pools at the bottom and warm air rises and stays. Inuit families have used igloos as winter shelters for centuries, and they work brilliantly - proof that with the right design, even snow can keep you warm.
