The Gurley Model 4301 Permeometer measures the porosity or air-permeability of materials where air flow is an important characteristic relative to their use. These materials might be non-woven or woven textiles, filter and cloth felts, some types of blotting, saturating and absorbent bag papers as well as meshes. Conform to TAPPI T-251, ASTM D-737, DATM 70.0-70 and ISO 5636/1.