Bison wool

Bison wool refers to bison down — the fine undercoat that the American bison (Bison bison) grows beneath its coarse guard hair. An adult produces around 2–3 kg of guard hair per year but only about 500 grams of down. The fibres measure 15–18 µm — comparable to high-grade cashmere (14 µm) and significantly finer than extra-fine merino (from 19 µm).

The bison naturally sheds its winter coat in spring; the fibres are collected from ranch fences and brush or combed out during routine herd handling — no shearing is involved. Each fibre has a hollow core (like feather down) that traps air and nearly doubles insulation performance: bison wool is roughly twice as warm as sheep wool at equal weight. Brands such as United By Blue, The Buffalo Wool Co. and Bison Gear use the fibre for base layers, beanies, gloves and socks.

• Fineness 15–18 µm — in the cashmere range
• Hollow-cored fibre — nearly double the warmth of sheep wool
• Collected or combed — no shearing required
• Very limited availability — premium price