Ghoms are hand-knotted on vertical looms using warps made of cotton or (rarely) silk. Almost all production is concentrated in the city; specifically, they are made in private homes where there are usually two looms. The foundation may be either cotton or silk, and both materials may be used, either independently or in conjunction, for the pile. The weave is among the finest, with some 250 to 300 Persian knots per square inch on woolen items, and 600 or more on silk; good quality materials are normally used.