GB/T 2951.21-2008 standard covers specific test methods for resilience mixtures of cable and optical cable insulation and sheath materials. It mainly includes ozone resistance test, thermal extension test and mineral oil immersion test. The standard applies to cables and optical cables for power distribution and communication, especially for ships and offshore cables. Ozone resistance test is used to evaluate the tolerance of materials in an ozone environment; thermal extension test measures the ductility of materials at high temperatures; mineral oil immersion test checks the resistance of materials to immersion in mineral oil. The standard provides systematic test methods and requirements to ensure the Reliability of cable and optical cable materials in actual use.