FYI: this was accidently found by UK scientists studying Global Warming by counting Polar Bear populations in the Arctic. They tried conventional photography by air, but just got white bears on white snow. They then tried IR film, but Polar Bears are too well insulated to show up as hot. They then tried a special UV TV camera, and voila, they found out the above info.
FYI: Fiber-optic Fur: Unlike other arctic mammals, Polar bears never shed their coat for a darker shade in the summer. The fur absorbs ultraviolet light. The hair does not have fiber-optic properties nor does it transmit light or heat to the skin (an urban legend). The thick undercoat does however insulate the bears to the point where they overheat at temperatures above 10 °C (50 °F). It also renders them nearly invisible in the infrared; only their breath and muzzles can be seen. Growing through the undercoat is a relatively sparse covering of hollow guard hairs about 6 inches long. These guard hairs are stiff, shiny and erect, and stop the undercoat from matting when wet. The water is then easily shaken off before it can freeze. The bear also rolls in snow to blot up moisture in the coat. http://www.sheppardsoftware.com/content/animals/animals/mammals/polarbear.htm