Air permeance of paper and paperboard (Sheffield method) , Test Method 547 om-23
This method is used to measure the air permeance of a circular area of paper using a pressure differential of approximately 10 kPa (1.5 psig). In order to accommodate a wide range of paper products, rubber clamping plates are available for five commonly used orifice diameters: 9.5 mm (0.375 in.), 19.1 mm (0.75 in.), 38.1 mm (1.50 in.), 57.2 mm (2.25 in.), and 76.2 mm (3.00 in.). The air flow range for this method is 0 to 3348 mL/min (0 to 400 Sheffield units). Instruments are available with either variable area flowmeters (glass tubes with internal tapers and floats) or electronic mass flowmeters.