Denim is a durable, rugged cotton twill fabric that's most commonly used in jeans, jackets and overalls, as well as in other types of clothing.
Denim is created by a weaving process in which the weft passes under two or more warp threads. This twill weaving produces the familiar diagonal ribbing of the fabric, which distinguishes denim from cotton duck. It is characteristic of any indigo denim that only the warp threads are dyed, whereas the weft threads remain plain white. As a result of the warp-faced twill weaving, one side of the fabric shows the blue warp threads, the other side shows the white weft threads.