Rubber refers to a material that is capable of recovering from large deformations quickly and forcibly, and can be, or already is, modified to a state in which it is essentially insoluble (but can swell) in a boiling solvent such as benzene, methyl ethyl ketone or ethanol toluene azeotrope.

See also:
"Rubber" is in the NAICS Code "316211"
(Rubber and Plastics Footwear ManufacturingOvershoes, plastics or plastics soled fabric upper, manufacturing)

"Rubber" is in the CPC Code "27992"
Rubber thread and cord, textile covered; textile yarn and strip, impregnated or covered with rubber or plastics