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.

Yak down is a very warm fiber that’s also lightweight and soft. It’s a more affordable alternative to the rare qiviut (musk ox down). Yaks are primarily raised by nomadic Tibetan and Mongolian families. Their wool is combed once per year in the springtime. Some advantages of yak wool: Yak wool is 66% more breathable and 40% warmer than merino, …

These are the warmest sweatpants I’ve found this year.

These are the warmest hoodies I could find in 2019:

These are the warmest men’s sweaters I’ve found for 2019: