Blubber is the primary fat storage layer for some mammals, especially for those that live in water. It is particularly important for species that feed and breed in different parts of the ocean. During these periods, the animals metabolize fat. Blubber may save energy for marine mammals, such as dolphins, in that it adds buoyancy while swimming.
Blubber has advantages over fur (as in sea otters) in that, though fur retains heat by holding pockets of air, the air expels under pressure (i.e., when the animal dives). Blubber, however, does not compress under pressure. It is effective enough that some whales can dwell in temperatures as low as 4 °C (40 °F). While diving in cold water, blood vessels covering the blubber constrict and decrease blood flow, thus increasing blubber’s efficiency as an insulator.
Yup. https://en.wikipedia.org/wiki/Blubber