When integrity testing a filter it is important to use a clean and dry gas, preferably Nitrogen but otherwise compressed air. Contaminents in the gas such as oil, water vapour etc can affect the result and if constant results are desired then ideally dry, sterile filtered  Nitrogen should be used. Compressed air is permiable through rubber where Nitrogen is far far less so. CFS has its own Nitrogen generation capability to gain the optimum advantage in any test work