Gurley method:
The air is compressed by the weight of a vertical cylinder floating in a liquid. A test piece is in contact with the compressed air and the cylinder falls steadily as air passes through the test piece. The time for a given volume of air to pass through the test piece, the air resistance is measured and from this the air permeance is calculated.
This method is applicable for porous materials such as paper, board, textile, non-woven fabric, plastic film etc.
Guiley air permeability tester YG462