n A reduction in the modulus and tensile strength of a rubber vulcanizate as a result of prolonged thermal ageing. It occurs in sulfur vulcanized rubbers containing polysulphide crosslinks that have been overcured or during exposures to temperatures above 150°C. Reversion is due to a breakdown in the network structure, probably as a result of crosslink forming cyclic structures. Reversion can be also defined as the recombination of the hydrolysis products of polysaccharides. The softening of vulcanized rubber (usually natural but sometimes synthetic rubber) when heated too long or at too high a temperature. Reversion is evidenced by increase in extensibility, decrease in tensile strength, and lowering of the stress to produce a given elongation. Extreme reversion usually results in tackiness (Harper CA (ed) (2002) Handbook of plastics, elastomers and composites, 4th edn. McGraw-Hill, New York).