Fiber refers to a class of materials that are long, thin and cylindrical in shape. In textiles, fibers refer to natural or synthetic strands used for weaving, knitting, or spinning into yarn or thread. Common sources of fiber include cotton, wool, silk, hemp, and rayon. Fiber can also be used as a nutritional term referring to the dietary components that are not broken down by digestion and pass through the body unchanged. These fibers promote proper bowel function and help prevent constipation or other digestive issues.