This test method covers the measurement of the air permeability of textile fabrics. The reate of air flow passing perpendicularly through a known area of fabricc is adjusted to obtain a prescribed air pressure defferential between the two fabric surfaces. From this rate of air flow, the air amount (unit: cm3/s/cm2 etc.), which passes the rest specimen, is obtained. The air permeability is a very important factor in the performance of some textile materials. Especially, it is taken in to consideration for clothing, parachutes, sails, vacuum cleaner, fabric for air bags and industrial fabrics. The air permeability is mainly dependent upon the fabric’s weight and construction (thickness and porosity).