Blue whale has the most fat of any animal according to a study of 49 mammal species. Blue whales can weigh up to 180 tons and contain over 35% body fat. Marine mammals like whales have a thick layer of blubber, which is fatty tissue that provides benefits like insulation. Bowhead whales in northern waters need especially thick blubber, almost half a meter, to survive in the cold environment as the blubber can make up 43-50% of their body mass.