The direction in which the pileThe surface of a rug or carpet, made of upright fibers in cut tufts or loops. In a hand-knotted rug it is formed by the cut ends of thousands of wool or silk knots tied onto the warp row by row, trimmed lightly during weaving and given its final height by shearing at finishing. Pile thickness, measured from the back of the rug to the top of the pile, typically runs from low, about 1/8 to 1/4 inch (3 to 6 mm), to high, about 1/2 to 5/8 inch (13 to 16 mm). Fine, dense designs are cut short to keep the pattern sharp; higher pile suits traffic and heavy furniture, lower pile suits door clearance and humid rooms. fibers lie, which can be found by feeling the rug by hand. The rug looks lighter or darker depending on the direction from which it is viewed relative to the nap. Wiping and brushing are done with the nap, since going against it works liquid deeper into the pile, and vacuuming runs side to side rather than head-on against the nap, so the fibers are not pulled.