Most textiles are produced by twisting fibers into yarns and then knitting or weaving the yarns into a fabric. Textiles are made up of natural or synthetic fibers. Many fibers are found in nature and come from plants, animals, and minerals. Plants provide more textile fibers than do animals or minerals. Examples of plant fibers are cotton which produces soft, absorbent fabrics and linen which is produced from fibers of the flax plant. The main animal fiber used for textiles is wool. Another animal fiber is silk which produces one of the most luxurious fabrics. Sheep supply most of the wool, but members of the camel family and some goats also furnish wool. Most manufactured fibers are made from wood pulp, cotton linters, or petrochemicals made from crude oil and natural gas. The chief fibers manufactured from petrochemicals include nylon, polyester, acrylic, and olefin. Woven textiles are made of two sets of yarns - the lengthwise set is called the warp and the crosswise set is called the weft. The textile industry also produces other classes of fabrics such as knits, felts, braids and nonwovens. Contract textiles are available in a wide variety of weaves and fibers and are often treated with flame retardents and soil and stain repellents.