Dense Underfur Insulates

a white reindeer without antlers looks toward the camera in a snowy environment

Biological Strategy

AskNature Team

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Protect From Temperature

Many living systems function best within specific temperature ranges. Temperatures higher or lower than that range can negatively impact a living system’s physiological or chemical processes, and damage its exterior or interior. Living systems must manage high or low temperatures using minimal energy, which often requires controlling responses along incremental temperature changes. To do so, living systems use a variety of strategies, such as avoiding high or low temperatures, removing excess heat, and holding heat in. Insulation is a well-known example of managing low temperatures by retaining heat using thick layers of hair, fur, or feathers to hold warm air next to the skin.

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The coat of a reindeer insulates against polar cold with the help of dense underfur that traps air.

Image: Alan Wilson /

Woodland Caribou, Stone Mountain Provincial Park, British Columbia

Image: Alan Wilson /

Woodland Caribou, Stone Mountain Provincial Park, British Columbia

Image: Alan Wilson /

Mountain Caribou (Male), Stone Mountain Provincial Park, British Columbia

“Naturally, animals that live in polar regions have the warmest coats of all. The reindeer’s coat combines long, water-repelling guard hairs with an extremely dense underfur, deep-piled like a shag carpet.” (Foy and Oxford Scientific Films 1982:84)

“The winter fur of adult reindeer consisted of thick guard hairs with air-filled cavities and an underfur of thin and woolen hairs…The density of guard hairs varied considerably and averaged 2000/cm² and 12 mm on the legs, 1000/cm² and 30 mm on the abdomen, and 1700/cm² and 30 mm on the back. The corresponding count on the back of calves was 3200/cm² and 10 mm…All hairs were wool-like and hollow…The thick underfur is very important, since it effectively prevents air movement within it and thus reduces heat dissipation…[T]he results suggest that the prime mechanism by which adult reindeer thermoregulate in a cold environment is insulation.” (Soppela et al. 1986:275, 277)