Denim is a sturdy cotton warp-faced textile in which the weft passes under two or more warp threads, which creates a subtle diagonal ribbing pattern. The cotton twill fabric is warp-facing, meaning that the weft threads go under two or more warp threads, and the warp yarns are more prominent on the right side. The diagonal ribbing is what makes denim fabric different from canvas or cotton duck, which is also a sturdy woven cotton fabric.