GB/T 30801-2014 provides for the determination of the moisture permeability performance of building materials and products by the box method. It specifies the structure and parameter requirements of the box test device, including key indicators such as Humidity control and air circulation. Detailed description of the method of installing the test piece in the test chamber. Measurement unit time through the test piece by controlling the Humidity difference on both sides of the box. This accurately evaluates the moisture permeability performance of the material, provides a scientific basis for the selection of moisture-proof, waterproof and thermal insulation materials in building design, and helps to improve the indoor environment mass and structural durability of the building.