GB/T 20643.3-2025 "Special Environmental Conditions - Environmental Testing Methods - Part 3: Artificial Simulation Test Methods and Guidelines for Polymer Materials" applies to the environmental adaptability testing of polymer materials such as plastics, rubber, and coatings. It replaces the previous version and expands the technical coverage. The standard specifies artificial simulation test methods for six special environments: dry heat, dry desert, plateau, damp heat, damp marine, and cold. It introduces new combined tests for temperature/low pressure and salt spray/temperature/humidity/solar radiation. The standard defines test parameters, assessment indicators, and recommended durations for each environment, adjusts the sand and dust test methods, and provides guidelines for selecting test programs and determining severity levels. It offers a unified basis for the design, application, and evaluation of polymer materials in special environments.