Resistance of paper to passage of air (high-pressure Gurley method), Test Method TAPPI/ANSI T 536 om-22
This method is used to measure the air resistance of approximately 6.4 sq. cm. (1 sq. in.) circular area of paper using a pressure differential of approximately 3 kPa. The recommended range of this instrument is for papers that require 10 or more seconds for 10 mL of air to pass through. Refer to the manufacturer's instructions for the upper range limits. For more permeable papers, other techniques are preferable. Instruments are available with automatic timing devices.