This Pakistan Standard prescribes the methods of mea suring the air permeability in terms of the number of cubic feet of air passing through one square foot of fabric per minute when the air pressure difference across the fabric is equal to half an inch of water. It is applicable at low air pressure to all types of fabrics and to a variety of other permeable materials in sheet form.
PS 150-1961 history
1961PS 150-1961 Method for Determination of the permeability of fabrics to air at low pressures,