Coagulated latex of a variety of plants, mainly from the New World. Most important is Para rubber, which derives from the tree Hevea brasiliensis of the spurge family. It was introduced from Brazil to se Asia, where most of the world supply is now produced, the chief exporters being Peninsular Malaysia, Indonesia, Sri Lanka, Cambodia, Thailand, Sarawak, and Brunei. At about seven years the tree, which may grow to 20 m/60 ft, is ready for “tapping”. Small incisions are made in the trunk and the latex drips into collecting cups. In pure form, rubber is white and has the formula (C5H8)n.
Other sources of rubber are the Russian dandelion Taraxacum koksagyz, which grows in temperate climates and can yield about 45 kg/100 lb of rubber per tonne of roots, and guayule Parthenium argentatum, a small shrub of the Compositae family, which grows in sw us and Mexico.
Early uses of rubber were limited by its tendency to soften on hot days and harden on colder ones, a tendency that was eliminated by Charles Goodyear's invention of vulcanization 1839.
In the 20th century, world production of rubber has increased a hundredfold, and World War ii stimulated the production of synthetic rubber to replace the supplies from Malaysian sources overrun by the Japanese. There are an infinite variety of synthetic rubbers adapted to special purposes, but economically foremost is sbr (styrene-butadiene rubber). Cheaper than natural rubber, it is preferable for some purposes; for example, on automobile tires, where its higher abrasion-resistance is useful, and it is either blended with natural rubber or used alone for industrial molding and extrusions, shoe soles, hoses, and latex foam.Latex from trees (especially trees of the genera Hevea and Ficus); SYN. India rubber, gum elastic, caoutchouc.

Slang term for a condom.

1. Made of rubber and therefore water-repellent; SYN. rubberized.
2. (Informal) No valid; SYN. no-good.