How do polar bears stay warm?

This 25 February 2019 video says about itself:

How does a polar bear stay warm? | Natural History Museum

There is more to polar bear fur than meets the eye. Mammals Curator Roberto Portela Miguez explains.

For engineers, polar bear hair is a dream template for synthetic materials that might lock in heat just as well as the natural version. Now, materials scientists have developed such an insulator, reproducing the structure of individual polar bear hairs while scaling toward a material composed of many hairs for real-world applications in the architecture and aerospace sectors: here.