Which marine animal has the thickest blubber?

The marine animal with the thickest blubber is the bowhead whale. Its blubber can reach roughly 40 to 50 centimetres in thickness, an extraordinary insulation layer for a whale that lives year-round in Arctic and sub-Arctic waters.

Bowheads face near-freezing seas and seasonal ice, so their blubber serves several purposes: it conserves body heat, stores energy, provides buoyancy, and cushions the body. Their massive skulls also help them break through sea ice to reach air.

The species is not the largest whale—that title belongs to the blue whale—but it is exceptionally stocky and heavily insulated. Bowheads can grow to about 18 metres and have a broad head that may account for nearly one-third of their body length.

Commercial whaling reduced some bowhead populations dramatically, especially during the nineteenth and early twentieth centuries. The whale is now protected, although it still faces threats from climate change, ship traffic, entanglement, noise, and changing Arctic food webs. Right whales can also have very thick blubber, but bowheads are the standard answer to this record question.