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 are often used, as these fibers are less expensive than wool. The pile usually consists of twisted tufts which are typically heat-treated to maintain their structure. Carpets are used for a variety of purposes, making a room more comfortable as a place to sit on the floor reducing sound from walking and adding decoration or colour to a room. Carpets can be made in any colour by using differently dyed fibers. Carpets can have many different types of patterns and motifs used to decorate the surface.