The ASTM F1608-21 standard defines a test method for the microbial grade of porous Encasement materials. The microbial barrier performance of materials is evaluated using the exposure chamber method. This method determines the microbial barrier effect of porous materials under specified conditions and is used to compare the relative potential of different materials in preventing bacterial contamination of sterile contents. The experimental results described in the standard show that the logarithmic reduction value (LRV) of materials that pass the test ranges from 1.7 to 4.3. This method is suitable for testing the ability of airborne bacteria to pass through porous materials, but cannot fully predict performance in actual sterile Encasement applications. Users are required to follow appropriate safety measures and further validate on a case-by-case basis.