Superwash
Superwash is a treatment for wool yarn that removes the outer scales of the wool fiber, allowing the yarn to withstand regular machine washing without felting.
Explanation
Superwash treatment makes wool yarn machine-washable by either removing or coating the microscopic scales on the surface of the wool fiber that normally interlock and cause felting when wool is exposed to heat, moisture, and agitation together. This is usually done chemically (chlorine treatment) or by applying a thin polymer coating. Superwash yarn is popular for socks, baby garments, and other items that are washed often, but it loses some of the natural elasticity and loft of untreated wool, and can therefore 'grow' slightly in size over time.