Air permeability of porous paper, fabrics, and pulp handsheets

TAPPI T251 Air permeability provides for evaluation of the air permeability of highly porous papers, other fiber webs and fabrics and for formation of special handsheets to evaluate the potential for development of this property in raw materials. The permeability is measured by determining air flow through the sheet at a specified pressure drop. The sheet formation is based on conventional procedures, with special provisions for handling sheets of low porosity.