The pelts are composed of hairs approximately 100–150 μm in diameter and 6–7 cm long. In addition to the hair, there is a dense fur approximately 1 cm long and ¼ the diameter of the hair located at the base of the hair next to the skin. The skin itself appears black in color. Observations of individual hairs under a light microscope indicate that they are transparent cylinders with hollow translucent cores and solid tapered ends. They contain no pigmentation. Comparison with a drawn quartz tube of approximately the same dimensions under UV and visible illumination did not indicate any observable differences in transmission or refraction. Except for the structure of the inner core of the hairs, they are visually indistinguishable.
furs have excellent thermal insulation properties. Conduction is quite low for the hairs themselves. A count of only 100 hairs/cm2 provides excellent protection against convection loss and wind chill. The hide is covered with a thin dark layer or skin. This layer is less than 1 mm thick, and the hairs appear to terminate in it. The hide under this layer is light tan in color.
Polar bear in natural light
Transverse sections of polar bear hair
Information Source: https://www.osapublishing.org/ao/fulltext.cfm?uri=ao-19-3-339&id=23715
