The ISO 5636-3:2013 standard specifies a method for determining the air permeability of paper and Cardboard using the Bendtsen method, which is suitable for paper and Cardboard with a Porosity between 0.35 µm/(Pa · s) and 15 µm/(Pa · s). This method is used to calculate Porosity by measuring the flow rate of air through paper at a constant pressure difference through a Bendtsen device. This standard does not apply to paper and Cardboard with rough surfaces. The Bendtsen method is easy to operate and has good results Repeatability. It is widely used in the quality control of paper and Cardboard, especially in the fields of Encasement, printing and filtrating materials.