Polar Bear
For polar bears, fat is definitely where it's at. To keep warm when the temperature dips to 50 degrees below zero Fahrenheit, these BIG bears (and we mean big -- males max out at 1,700 pounds) have a four-inch layer of insulating fat underneath their skin.
Another cool thing about polar bears: Their fur isn't white! Each long hair is actually a clear, hollow tube that reflects light--and makes the animal disappear into the snow so that his prey (mainly seals) can't see him coming.