DIN 7724, Supplement, February 1972 gives this definition: "Elastomers are high-polymer materials, crosslinked in a wide mesh up to decomposition temperature. At low temperatures they display elastic properties like steel. At high temperatures they do not flow viscously, but are elastic like rubber from 20 °C or below up to decomposition temperature. This elasticity akin to rubber is characterized by largely temperature-independent values of the modulus of shear from around 0.1 to 100 N/mm² and great reversible deformability." Their rubber-elastic properties make elastomers a preferred choice as materials for secondary seals.