FiberFibers are a class of materials that are continuous filaments or discrete elongated pieces. As they occur in nature, they are important constituents of living things, as well as non-living mineral materials. Natural and man-made fibers are, in turn, often used in the manufacture of other materials.

Fibers are classified in several ways. First of all, any fiber produced by plants, animals and geological processes is considered natural fibers. Those composed of cellulose and lignin are considered vegetable or plant fibers. Some examples include the dietary fiber of vegetable foods, cotton for clothing, or hemp or flax for cordage. The fibers within and produced by animals may be far more complex with respect to their protein structures and functions. Some examples include insect and arachnid silks, animal tendon sinews and insulatory hair coatings such as wool and mohair. Finally, there are some filamentous mineral fibers in nature; perhaps the most common are asbestos and some naturally occurring silica-based glass fibers.