Full definition
A reversible physical phenomenon in which polychloroprene (neoprene) rubber molecules slowly align into ordered crystalline regions when stored or operated at temperatures between approximately 0°C and -10°C (rate depends on grade), causing progressive stiffening, hardening (+10-30 Shore A increase), loss of elasticity, and increased brittleness. Unlike thermal degradation, crystallization is fully reversible — heating the part to 60-80°C for 30-60 minutes melts the crystallites and restores original properties. The rate of crystallization varies significantly by neoprene type: W-types (standard) crystallize fastest; G and GN types (modified crystallization grades) are specifically formulated with co-monomers (thiuram/sulfur modified or gel/sol types) to resist crystallization and maintain flexibility at low temperatures. For applications requiring sustained low-temperature service (cold storage, arctic environments, winter outdoor exposure), specify GN or GNA grades or consider EPDM as an alternative. Per standard polychloroprene polymer datasheets. Crystallization is uniquely characteristic of CR — no other common industrial rubber exhibits this phenomenon.