The Sweater Stone is a piece of light pumice, volcanic rock which is made up of hundreds of tiny holes. When you rub the stone over the surface of a piece of woollen material that has developed unwanted pilling, the sharp edges of the holes cut it off. As the Sweater Stone gradually wears away, new micro-holes continually appear, so the stone sharpens itself. The smell of the stone is a result of its volcanic origin & will not transfer to the wool. When regularly used, will last many years.