How do sea otters keep warm in cold water?

Sea otters have a dense coat of fur that helps them stay warm in cold water. Their fur is the thickest of any animal and traps air close to their skin, providing insulation. Unlike most marine mammals, sea otters do not have a layer of blubber for warmth; instead, their fur and high metabolism are key to keeping them warm. Sea otters are also known for using tools, such as rocks, to break open shellfish, and they often float on their backs in kelp forests, which further insulates them from the cold water.