In terms of fineness, any wool fiber that has a diameter of 20µ (microns) or less will feel very soft to the touch.

Qiviut (pronounced “kiv-ee-ute”) is the name for the downy hair of the musk ox. It is the warmest fiber in the world — about eight times as warm as sheep’s wool. Musk oxen live in Alaska and Canada where temperatures sometimes drop to –100ºF (-73ºC), so they need protection. The Inuktitut name for the musk ox is “umingmak” meaning the …

Camel wool is a very soft, insulating fiber. It ranges in size from 15 to 22 microns — putting it in the ultrafine or superfine categories.

Bison down is a very warm, insulating fiber. It is also very durable for such a soft fiber.