fur

thumb|300px|Like many mammals, grizzly bears are covered in thick fur. A fur is a soft, thick growth of hair that covers the skin of almost all mammals. It consists of a combination of oily guard hair on top and thick underfur beneath. The guard hair keeps moisture from reaching the skin; the underfur acts as an insulating blanket that keeps the animal warm.

The fur of mammals has many purposes: protection, sensory, waterproofing, and camouflaging, with the primary purpose being thermoregulation. The types of hair include definitive, which may be shed after reaching a certain length; vibrissae, which are sensory hairs and are most commonly whiskers; pelage, which consists of guard hairs, under-fur, and awn hair; spines, which are a type of stiff guard hair used for defense in, for example, porcupines; bristles, which are long hairs usually used in visual signals, such as the mane of a lion; velli, often called "down fur", which insulates newborn mammals; and wool, which is long, soft, and often curly.