* Humans: We have hair (though often less than other mammals) that helps regulate our body temperature.
* Dogs and Cats: Their fur is a major part of keeping them warm in cold weather.
* Bears: Bears have thick fur that provides excellent insulation during the winter.
* Polar Bears: They have incredibly thick fur and a layer of blubber for extreme cold protection.
* Whales: Though not technically hair, whales have blubber that acts as insulation in the ocean.
Do you have a specific mammal in mind? Let me know, and I can tell you more about its insulation!