Fur and skin

A polar bear's fur is white (individual hairs are transparent like the water droplets that make up a cloud) and provides good camouflage and insulation. It may yellow with age. The fur acts as miniature greenhouses, and turns sunlight into heat, which is absorbed by the bear's black skin. Stiff hairs on the pads of its paws provide insulation and traction on ice.

Unlike other Arctic mammals, polar bears do not shed their coat for a darker shade in the summer. It was once conjectured that the hollow hairs of a polar bear coat acted as fiber-optic tubes to conduct light to its black skin, where it could be absorbed - a theory disproved by recent studies.[7] The thick undercoat does, however, insulate the bears: they overheat at temperatures above 10 °C (50 °F), and are nearly invisible under infrared photography; only their breath and muzzles can be easily seen.[8] When kept in captivity in warm, humid conditions, it is not unknown for the fur to turn a pale shade of green. This is due to algae growing in the guard hairs - in unusually warm conditions, the hollow tubes provide an excellent home for algae. Whilst the algae is harmless to the bears, it is often a worry to the zoos housing them, and affected animals are sometimes washed in a salt solution, or mild peroxide bleach to make the fur white again.

Size and weight

Polar bears rank with the Kodiak bear as among the largest living land carnivores, and male polar bears may weigh twice as much as a Siberian tiger. Most adult males weigh 300-600 kg (660-1320 lbs) and measure 2.4-3.0 m (7.9-10.0 ft) in length. When standing upright, an adult male can stand up to 3.35m (11.5 feet). Adult females are roughly half the size of males and normally weigh 150-300 kg (330-660 lbs), measuring 1.9-2.1 m (6.25-7 ft). At birth, cubs weigh only 600-700g or about a pound and a half.