Fibre or fiber 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 fibres 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. Fibres are often used in the manufacture of other materials.
Fibres used by man come from a wide variety of sources.
- Natural fibres include those produced by plants, animals, and geological processes. They can be classified according to their origin:
- Vegetable fibres are generally based on arrangements of cellulose, often with lignin: examples include cotton, linen, hemp, jute, flax, ramie and sisal. Plant fibers serve in the manufacture of paper and cloth.
- Animal fibres consist largely of particular proteins. Instances are silk, sinew, catgut and hair (including wool).
- Mineral fibres comprise asbestos, the only naturally occurring mineral fibre.
- Man-made fibres may come from natural raw materials or from synthetic chemicals.
- Many types of fibre are manufactured from natural cellulose, including rayon, modal, and the more recently developed Lyocell. Fibreglass and optical fibre, which are made from purified natural quartz, are also man-made fibers that come from natural raw materials.
- Synthetic fibres are a subset of man-made fibres, which are based on synthetic chemicals (often from petrochemical sources) rather than arising from natural materials by a purely physical process. Such fibres are quite often made from nylon, polyester, or acrylic polymers, although pure polyacrylonitrile fibres are used to make carbon fibre. More exotic fibres have strong bonding between polymer chains (e.g. aramids), or extremely long chains (e.g. Dyneema or Spectra). Elastomers can even be used, e.g. spandex.
- The spelling fibre is used in Commonwealth countries, and is sometimes used in the United States as well.