Blubber is a fat layer underneath an animal’s skin. Blubber is composed of fat-filled cells and functions both to insulate and to store food reserves.
Many whales migrate from feeding to breeding grounds each year. During the several months they are in their feeding grounds, they take in enough food to last for the entire year. Whales feed little, if at all, at their breeding grounds, instead relying on energy derived from their blubber.
In addition to storing energy, blubber can also accumulate toxic contaminants. If a whale or seal ingests pollutants, those pollutants may be stored in the blubber layer, where they can harm the animal as it uses those energy reserves.