Instead of fur, whales have a thick layer of fat, called blubber, round their bodies. Blubber keeps them warm and helps support their large bodies in the water. Some whales have blubber 38 cm (15 in) thick. Whales have long been hunted for the valuable oils in their blubber. A blue whale's blubber can weigh as much as four tractors and may contain over 120 barrels of oil.