Which animal has the densest fur?

Sea otters have the densest fur of any mammal: an estimated 850,000 to one million hairs per square inch. A dense underfur under longer guard hairs keeps them warm in cold Pacific water.

What's actually true

Sea otters have the densest fur of any mammal. Sea otter fur packs an estimated 850,000 to one million hairs into every square inch, more than any other mammal. A dense underfur sits beneath a layer of longer guard hairs. That thick coat is how a sea otter stays warm in cold Pacific water.

Takeaway: A patch of sea otter fur the size of a large postage stamp holds up to a million hairs.

Why people believe it

Most people guess a cold-climate land animal such as a polar bear, a chinchilla or a yak, because thick fur and snow go together in our heads. The sea otter is less obvious: it looks sleek when wet and lives in water, where you might expect fat to do the insulating, as it does for seals and whales. Sea otters have little blubber, so their fur carries that job, which explains its extreme density.

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