A carpet is a textile floor covering consisting of an upper layer of pile attached to a backing. The pile is generally either made from wool or fibers such as polypropylene, nylon or polyester and usually consists of twisted tufts which are often heat-treated to maintain their structure. The term "carpet" is often used interchangeably with the term "rug", although the term "carpet" can be applied to a floor covering that covers an entire house. Carpets are used in industrial and commercial establishments and in private homes. Carpets are used for a variety of purposes, including insulating a person's feet from a cold tile or concrete floor, making a room more comfortable as a place to sit on the floor (e.g., when playing with children or praying in Arabic culture) and adding decoration or colour to a room.