DIN 53120-2
DIN 53120-2 Testing of paper and board - Determination of air permeability - Part 2: Method for medium rates of air permeability according to Schopper
standard by Deutsches Institut Fur Normung E.V. (German National Standard), 05/01/2008
standard by Deutsches Institut Fur Normung E.V. (German National Standard), 05/01/2008