Wool is the fine, soft, wavy hair that forms all or part of the protective coat of domestic sheep.  It has been harvested from ancient times to provide clothing and household coverings and holds an important place in today's textile trade because of its properties of insulation, absorbency, resilience, and ability to take dye well.
A fiber of wool is made up of long, narrow, cigar shaped cells that over lap each other creating a scaly pattern.  This provides a means for the fibers to lock together making it easier to spin.
Among the 450 breeds of domestic sheep in the world, great differences exist in the amount and the kind of wool produced. Merino sheep, for instance, produce extremely fine (in fiber diameter) and soft wool used for apparel. "Down" breeds, such as Southdown, Hampshire, and Suffolk, produce short, spongy wool suitable for specialty lines of knitwear and fabrics. Such breeds as Romney, Corriedale, Border Leicester, English Leicester, and Lincoln produce long, medium to coarse wool, which is used for knitwear, tweeds, and blankets. ⁽¹⁾