Sea otters have the world's thickest fur
Sea otters don't just have the densest fur of all otters — they have the densest fur of all animals! They have as many as 1 million hairs per square inch on the densest parts of their body. They need every last hair because they are the only marine mammal to not have a layer of blubber as insulation against the freezing ocean water. Their fur protects them from the cold and keeps them waterproof.
So much hair requires a lot of grooming. Sea otters spend their time either eating, sleeping or grooming. When they're awake and not eating, they're grooming all that fur to keep as dry and warm as possible. There are just a few places on a sea otter's body that doesn't have such dense fur, and that includes their paws. This is one reason why they hold their paws up when resting — they need to keep them out of the water and conserve body heat.