Fiber or fibre is a class of materials that are continuous filaments or are in discrete elongated pieces, similar to lengths of thread. Fibers are of great importance in the biology of both plants and animals, for holding tissues together. Human uses for fibers are diverse. They can be spun into filaments, thread, string or rope. They can be used as a component of composite materials. They can also be matted into sheets to make products such as paper or felt. Fibers are often used in the manufacture of other materials.