Arctic marine mammals, like whales, seals and walruses, are warm blooded but spend most or all of their lives in the cold water. Heat loss is much greater in water than in air, and without a way to keep heat from leaving their bodies, they would freeze to death in water that is usually just above the freezing point.

To insulate them from the cold, these animals have a thick, dense layer of connective tissue and fat under their skin called blubber.

In other mammals (such as humans), fat may provide some insulation, but that is not its purpose. Fat stores energy, and insulation is provided by hair (or coats and thick sweaters). The blubber of Arctic marine mammals both stores energy and provides insulation.

The thickness of the blubber can vary from a couple of inches in smaller whales and seals, to over 12 inches / 30 cm thick on larger whales.

Blubber was important to Arctic native people because it provided both high energy food and oil for fuel, and this rich oil was the main reason for the whaling trade. Whale blubber was collected, then rendered down into oil in giant cauldrons. The whale oil was used as fuel in lamps, for making candles, and as lubricants for machinery.

As the whaling industry was responsible for the killing of hundreds of thousands of whales, it is somewhat ironic that the very blubber that allowed them to live, also led to their deaths.