One of my favorite adaptations that allow polar bears to survive in such harsh climates is the fact that their fur is actually clear, though of course it looks white from any distance. This allows their skin, which is black, to absorb as much heat as possible from the sun on sunny days. Every little bit counts when it is so important to gather heat energy.
Because of the difficulties of survival in the arctic, mother polar bears are also incredibly protective of their cubs and the cubs themselves are not weaned until usually two to two and a half years of age. At that time the mother chases them off but until that time she is extremely protective of them.