Fiber or fibre (from the Latin fibra) is a natural or synthetic string used as a component of composite materials, or, when matted into sheets, used to make products such as paper, papyrus, or felt. Fibers are often used in the manufacture of other materials.iber or fibre (from the Latin fibra) is a natural or synthetic string used as a component of composite materials, or, when matted into sheets, used to make products such as paper, papyrus, or felt. Fibers are often used in the manufacture of other materials.