Paper is composed of a mesh structure with an infinite number of through-holes, concaves, and closed spaces. Air permeability test measures resistance to air that passes through the specimen. There is a relationship between air permeability and paper density, formation, water absorption and printability. Air permeability is a measure of the porosity of paper. This machine measures the air permeability of porous materials including papers, filter paper and packaging paper. The inner cylinder of a specified mass gradually moves oil downward in the outer cylinder. The time necessary for a specified volume of air to pass through the specimen is measured by stopwatch.