Wool is a natural protein staple fiber that is produced by sheep. As is a biodegradable fiber, wool is a renewable resource that can be reprocessed and recycled. Wool has been grown for textile use for over 8,000 years and is most often used in upholstery and apparel. It is inherently resistant to stains, odors, and fire, as well as UV rays and static. Often used for acoustic purposes, wool fibers can absorb noise as well as large quantities of moisture vapor while maintaining a dry feel. Common types of wool include merino, cashmere, and mohair. The quality of wool is graded by color, and finesse, as well as the strength and length of the fibers.