The thick insulating underfur of an Arctic musk ox is called qiviut.
Qiviut is the soft, fine layer beneath the animal’s longer outer hairs. Musk oxen grow this dense undercoat before winter, and they shed it naturally in spring. The fibers help the animals withstand severe Arctic cold while using less energy than they would need if they relied only on body fat.
Qiviut is especially valued as a luxury natural fiber because it is warm, lightweight, and typically softer than sheep’s wool. People collect it from shed fibers, rather than normally shearing the animals. In Canada and Greenland, organized harvesting and processing support traditional and commercial crafts.
The term can also be spelled qiviuq in some Inuit-language contexts. It should not be confused with cashmere, which comes from goats, or lanolin, a waxy substance associated with sheep wool. The musk ox’s long guard hairs provide a weather-resistant outer layer, while qiviut supplies much of the fine insulation underneath.