Full definition
A polymer material that can be stretched to at least twice its original length and returns to approximately its original shape upon release of the deforming force — the defining characteristic that distinguishes rubber from plastics. Elastomers achieve this elastic behavior through long, flexible polymer chains with chemical cross-links (vulcanization) that act as memory points. Major families: natural rubber (NR, cis-1,4-polyisoprene), styrene-butadiene (SBR), neoprene/chloroprene (CR), nitrile (NBR), EPDM, silicone (VMQ), polyurethane (PU/AU/EU), fluoroelastomer (FKM), and butyl (IIR). Classification per ASTM D2000 / SAE J200 uses a two-letter system: first letter = heat resistance (A=70°C to J=275°C), second letter = oil resistance (A=no requirement to K=highest). Properties specified: hardness (Shore A), tensile strength (MPa), elongation (%), compression set (%), specific gravity, and temperature range. Global market: ~30 million tonnes/year, with NR and SBR representing over 60% of volume.