Nain rugs usually have a cotton foundation with a very soft wool or wool & silk pile. The majority of Nain rugs have at least some silk detail. Quality is measured not only in knots per square inch (KPSI) which averages about 300 but also in LAA. LAA is a Farsi term referring to the number of threads that make up each fringe. A Nain with a LAA of 9 is considered a good quality rug (yet is the lowest quality of true Nains) while a LAA of 4 the best. LAA is related to KPSI as it allows tighter knotting.