In the coldest parts of the world, insulation is essential for survival. One way is to have a good thick layer of blubber under your skin. But anyone that’s seen a walrus flopping across the beach knows that fat can have its downsides. To stay both warm and agile, fat won’t do. The Arctic fox can withstand polar winters, surviving long periods below -20 °C (-4 °F), thanks to some incredible adaptations.