On a spring day in Glacier Bay in Southeast Alaska, a raft of sea otters is floating near Bartlett Cove. The water is cold, but these otters aren't feeling it. Most marine mammals in Alaska retain their body heat with a thick layer of blubber. Sea otters are different. They don't have a lot of body fat and instead depend on thick, well-groomed fur. Otters have phenomenally thick fur. We humans have about 2,000 hairs per square inch on our heads. Dogs have as much as 60,000 hairs per square inch, and the luxurious coat of a cat can be five times that dense. A sea otter can have up to a million hairs per square inch - the densest fur coat of any animal in the world. Long, waterproof guard hairs protect dense underfur.
Hair that thick requires constant grooming. Otters groom themselves to dry their underfur and to distribute oil from their skin into the fur, making it waterproof. Air trapped in the fur keeps the otter's skin dry. The sea otter is essentially encased in a thick bubble of air, which insulates four times better than a similar layer of blubber.
Sea otters groom a bit like cats - licking themselves and rubbing their fur with their paws. But they do this while floating in the water, somersaulting and rolling to reach every part. They spend a lot of time grooming - their lives depend on it. They also spend a lot of time eating - A high metabolism is coupled with that thick fur to keep sea otters warm in frigid Alaska waters.