The GB/T 458-2008 standard specifies three methods for measuring the Porosity of paper and Cardboard: Gurley method, Schopper method and Bentsen method. This standard applies to paper and Cardboard with Porosity ranging from 1 × 10 ^ -2 μm/(Pa · s) to 1 × 10 ^ 2 μm/(Pa · s), but not to Cardboard with large surface roughness or difficult to firmly clamp. These measurement methods can evaluate the breathability performance of materials, which is of great significance for the design and quality control of Encasement materials and filtrate materials.