Cashmere wool, usually simply known as cashmere, is a fiber obtained from cashmere goats, pashmina goats, and some other breeds of goat. It has been used to make yarn, textiles and clothing for hundreds of years. Cashmere is closely associated with the Kashmir shawl, the word "cashmere" deriving from an anglicization of Kashmir, India, when the Kashmir shawl reached Europe in the 19th century. Both the soft undercoat and the guard hairs may be used; the softer hair is reserved for textiles, while the coarse guard hair is used for brushes and other non-apparel purposes. Cashmere is a hygroscopic fiber which essentially means that it absorbs water from the air. This helps regulate the body in both warm and cool temperatures by absorbing and releasing moisture based on the surrounding environment.

Fiber or fibre is a natural or artificial substance that is significantly longer than it is wide. Fibers are often used in the manufacture of other materials. The strongest engineering materials often incorporate fibers, for example carbon fiber and ultra-high-molecular-weight polyethylene.