Which marine mammal has the thickest blubber, reaching about 50 centimetres?

The bowhead whale has the thickest blubber of any marine mammal, with insulation reaching about 50 centimetres in some individuals. This thick fat layer helps the species survive in the Arctic and sub-Arctic oceans.

Bowhead whales spend much of their lives among sea ice, where water temperatures remain close to freezing. Their blubber provides thermal insulation, stores energy, and contributes to buoyancy. The species also has a massive skull and reinforced bones that allow it to break through ice several tens of centimetres thick to reach open water.

Bowheads are baleen whales, not toothed whales. They filter small prey such as copepods and krill from seawater through long plates of baleen. Their enormous, arched mouths help them process large volumes of water. Bowhead whales were heavily hunted commercially, but some populations have recovered under protection. They are also among the longest-lived mammals, with evidence suggesting that some individuals survive for more than 200 years.