(1) When you look at fur, especially the really dense fur of mammals, you look at that underfur , and it looks like down.(2) The fur of sea otters is very dense with an insulating underfur and a layer of long guard hairs over the top which trap a layer of air, adding further to the insulation.(3) The pelage lacks underfur and is usually some shade of brown.(4) The fur is composed of short, soft underfur covered by shiny guard hair.(5) The pelage of cane rats is unusual, made up of coarse, flattened or grooved bristle-like hairs, and lacking underfur .(6) A reindeer's key defense against the cold is an exceptional winter coat that has a fine underfur combined with long, hollow guard hairs that contain thousands of tiny, insulating air cells.(7) Gray wolves have a dense underfur layer, providing them with excellent insulation against cold conditions.(8) To the contrary, caribou underfur (like caribou skin in general) is not waterproof or water-repellent: moisture penetrates it easily.(9) Another characteristic of aquatic and semiaquatic mammals is that they are often well insulated; beavers accomplish insulation by a pelage that consists of long overfur (guard hairs) and dense underfur .(10) Beneath the overfur is short underfur of finer texture.
