On a knotted pile carpet (formally, a supplementary weft cut-loop pile carpet), the structural weft threads alternate with a supplementary weft that rises at right angles to the surface of the weave. This supplementary weft is attached to the warp by one of three knot types (see below), such as shag which was popular in the 1970s, to form the pile or nap of the carpet. Knotting by hand is most prevalent in Oriental rugs and carpets. Kashmir carpets are also hand-knotted.