Arctic fox

Polar fox fur provides the best isolation among all mammal furs. They tolerate temperatures down to – 94 Fahrenheit.

An excerpt from the article 22 facts about Arctic fox
They are perfectly anatomically adapted for this. Thick and multi-layered fur provides excellent thermal insulation. Additionally, the polar foxes are the only canines with fur-covered paws. Moreover, the polar fox has a low body area to volume ratio, as evidenced by its compact body shape, short snout and legs, and short, thick ears.