Arctic birds are specialists at keeping well-insulated. A thick layer of special, fine feathers, called down, traps warm air around the bird's body like a sleeping bag. As most Canadians know, down is the best insulating material available for parkas and sleeping bags. The world's finest down is produced by the eiders, Arctic ducks whose down is collected from their nests without harming the birds. This is the origin of the word "eiderdown" – another name for a comforter or duvet.

When it gets really cold, birds fluff out their feathers, creating even more space to trap warm air and to provide insulation from the cold outside. Ptarmigans take this one step farther, by growing extra feathers in the fall to give them maximum insulation for the winter.