This standard test method is used to evaluate the performance of distribution boxes and similar insulated Encasements. It is particularly suitable for high-value or high-risk items that require high-precision internal temperature control, such as biological materials, pharmaceuticals, and blood products. The test covers the insulation effect of Encasement under changing external Environmental temperature conditions, ensuring internal temperature stability. The method is suitable for Encasement with or without product payload. Because of the diversity of factors affecting the insulation performance, the test of actual Encasement is more reliable than that of simulated Encasement. This test method helps to determine the thermal stability of Encasement in actual use, but does not cover all use-related safety issues.