A natural fiber is a fiber that is produced by plants, animals, or geological processes. They can be used as components of composite materials, where the orientation of fibers affects the properties. Natural fibers can also be matted into sheets to make products such as paper or felt.

Natural fibers are categorized according to their origin:

• Vegetable fibers are based on arrangements of cellulose. Examples include cotton, flax, hemp, jute, and ramie.
• Wood fibers are also cellulose, but come from trees. Examples include softwood like pine and hardwood like oak.
• Animal fibers consist largely of particular proteins. Examples include silk, wool, angora, and alpaca.
• Mineral fibers are naturally occurring mineral fibers. Examples include asbestos.

Natural fibers have been used for thousands of years for clothing, shelter, tools, and more. They are generally biodegradable and renewable, making them a sustainable alternative to synthetic fibers.