Rayon is made from natural sources, but its conversion into fibers is a chemical process. This is why you may hear rayon described as a semi-synthetic fabric. Rayon is made from plant matter (cellulose fibers). At a high level, rayon is made by dissolving plant matter and converting the cellulose into filaments (continuous lengths of fibers) through a manufacturing process. Filament fibers can be cut into staple fibers if desired.
Plant matter, called wood pulp in the manufacturing process, can come from:
Trees: pine, spruce, hemlock, beech, oak, eucalyptus, birch; cotton linters (residual fibers attached to cotton seeds); bamboo.
Rayon was the first fiber manufactured. When it was developed in France in the 1890s it was known as "rayon", "art silk" and viscose (the manufacturer's trade name). In 1924, the fiber's name was changed to rayon, but only in the United States. In the 1920s, rayon became popular as an affordable alternative to silk.