A carpet is a textile floor covering typically consisting of an upper layer of pile attached to a backing. The pile was traditionally made from wool, but since the 20th century synthetic fibers such as polypropylene, nylon, or polyester have often been used, as these fibers are less expensive than wool. A prayer rug or prayer mat is a piece of fabric, sometimes a pile carpet, used by Muslims, some Christians, especially in Orthodox Christianity and some Baha’i during prayer.