Polar Bear Fur
Notice that these guard hairs from a polar bear are hollow, and that the hollow space has a rough interior.
The rough hollow space serves two purposes.
The trapped air inside the hair provides insulation to the bear. This is like holofil fibers for outdoor clothing.
The rough air/hair interface inside the hair scatters light so that the transparent material of the hair shaft appears white even when it is wet. (Just as snow which is made of transparent ice appears white because the air/ice interface scatters light.)
So the polar bear fur is an anti fiber optic, it scatters light away rather tan guiding it to the skin of the bear.
Optical microscope image of polar bear fur (The hair shaft is 0.15 mm in diameter.)
Phase contrast w/ the fur mounted in methyl cellulose.
Image taken by Kristina Yu
Image Copyright Exploratorium, 2007
Click to enlarge
Scanning electron microscope image of polar bear fur.
Image taken by Bill May, copyright Bill May 1998, used by permission.
Scientific Explorations with Paul Doherty
20 Sep 2007