This standard specifies three methods for determining the compression set of porous polymeric materials (such as sponge rubber latex and polyurethane foam). The main principle involves compressing the test specimen to a specified height at a constant temperature for a defined period, then unloading and allowing it to recover. The degree of deformation is calculated by measuring the permanent loss in thickness of the specimen. Key instruments required for performing this test include a compression device (consisting of two parallel plates with adjustable spacing) for applying load and maintaining the specimen under fixed deformation, and a constant-temperature oven capable of accurately controlling the temperature within ±1°C. This method provides a standardized quantitative test basis for evaluating the elastic recovery capability and durability of such materials.