Plastics are based on "polymers": long-chain carbon-based "organic" molecules. These chains are made up of repeating fundamental molecular elements, or "monomers". People have been using natural organic polymers for centuries in the form of waxes and shellacs, as well as fabrics and ropes, which are based on a plant polymer named "cellulose". By the early 19th century natural rubber, based on a polymer now known as "isoprene" and tapped from rubber trees, was in widespread use.

Eventually, inventors learned to improve the properties of natural polymers. Natural rubber was sensitive to temperature, becoming sticky and smelly in hot weather, and brittle in cold weather. In 1834, two inventors, Friedrich Ludersdorf of Germany and Nathaniel Hayward of the US, independently discovered that adding sulfur to raw rubber helped prevent the material from becoming sticky.

In 1839, the American inventor Charles Goodyear was experimenting with the sulfur treatment of natural rubber when, according to legend, he dropped a piece of sulfur-treated rubber on a stove. The rubber seemed to have improved properties, and Goodyear followed up with further experiments, developing a process known as "vulcanization" that involved cooking the rubber with sulfur. Compared to untreated natural rubber, Goodyear's "vulcanized rubber" was stronger; more resistant to abrasion; more elastic; much less sensitive to temperature; impermeable to gases; and highly resistant to chemicals and electric current.

Vulcanization still remains an important industrial process for the manufacture of rubber in both natural and artificial forms. Vulcanization creates sulfur bonds that link separate rubber polymers together, improving the material's structural integrity and its other properties.