The arctic fox is adapted to living in the northenmost areas of the world, and to withstand the cold in these areas. No other mammal has a fur that is so insulating. It doesn't have to increase its metabolism before the temperature goes under -4o degrees celsius. For the red fox, the temperature only has to go under -10 degrees celsius. At the same time the arctic fox is capable of storing fat, that for one part serves as heat insulation, and part as an energy reserve. This means that the arctic fox can go without food for several days.
The arctic fox changes it's fur between summer and winter
The arctic fox comes in two color variants. The regular white fox and a more bluish one. Both color variants change to a brown coat in the summertime. Living on the tundra, they will experience snow and ice in the winter, and brownish grass in the summer, so the color change helps them with season specific camouflage.