The coat of a muskox provides insulation via bilayer structure: a shaggy outercoat of guard hairs, and a thick silky undercoat.
“The musk ox has shaggy outer hair and a thick silky undercoat in which it can withstand any blast or blizzard…” (Foy and Oxford Scientific Films 1982:84)
Foy S, Oxford Scientific Films. The Grand Design: Form and Colour in Animals. Lingfield, Surrey, U.K.: BLA Publishing Limited for J. M. Dent & Sons Ltd, London; 1982. 238 p.