Nains are hand knotted on a vertical loom with a warp and weft of very fine cotton. The weft is often passed twice between the rows of knots thus giving this carpet durability. The pile is normally made of wool and is always very closely cropped. Silk is often used in the pile, serving to heighten the effect of some parts of the decorations thus giving it a certain gleam. Some rare examples exist which are made entirely of silk. Nains incorporate a Persian knot with very high densities ranging from 300 to 600 knots per square inch. There are varying sizes but the medium and large-size carpets are most common.