The weight of a pile yarn (including buried portions of the pile yarn) in a unit volume of carpet, which is expressed in ounces per cubic yard. Also called “Average pile yarn weight”. The closer the tufts are to each other, the denser the pile and the less weight each individual tuft has to support. Pile density is not only evaluated by the closeness of the tufts but also by the height and weight of the pile yarn. All other things being equal, the greater the pile density, the greater the wearability of the carpet and the longer it will last.