Domestic yaks are about the same size as ordinary cattle. The hair of the wild yak is black and short, except on the flanks and tail where it forms a long, shaggy fringe. Their dense coats and thick hides are necessary to protect them from the bitter cold of the high mountain country. When a yak lies down, it tucks its legs under its shaggy coat to keep them warm. Their horns spread outward and upward, and the head is held low like that of the bison.
Wild yaks are usually black.
The hides of both wild and tame yaks provide leather and the tails are valued as fly whisks in India. Domesticated yaks are also kept for milk and beef. The hair from the long fringes of the flanks is used in making cords and rope. The dried dung of the yak is the only obtainable fuel on the treeless Tibetan plateaus. Yaks moult once a year and the wool is made into blankets, tents, and packs.