This method measures the air permeability in terms of the number of cubic centimetres of air passing through one square centimetre of fabric per second when the differential between the air pressures on opposite sides of the fabric is equal to 12.7 mm of water. It is applicable to all types of fabrics and to a variety of other permeable materials in sheet form. (A test procedure utilizing a higher pressure (250 mm of water) is available in the method described in "High Pressure Porosity Instrument -- RAE Design", pamphlet AERO 1112/9R (Royal Aircraft Establishment, Farnborough, Hants, England).)

This method may require the use of materials and/or equipment that could be hazardous. This document does not purport to address all the safety aspects associated with its use. Anyone using this method has the responsibility to consult the appropriate authorities and to establish appropriate health and safety practices in conjunction with any existing applicable regulatory requirements prior to its use.