Aerodynamic Flow
A physical performance characteristic of porous materials determines how easily a fluid passes through a structure under pressure. For woven and knitted garments, air permeability measures the volume of air that passes vertically through a known area of fabric under a specific pressure drop over a set duration. The assessment halts when the fabric becomes completely non-porous or coated with an impermeable finish.
Inspected Tolerance
Measuring the air flow requires clamping the specimen securely across a test head to prevent edge leakage. This process employs a suction pump to draw air through the textile until the desired differential pressure is reached. Testing operators record the resulting velocity to calculate the average transmission rate across multiple fabric zones.
Apparatus Setting
Woven structures with high yarn counts and dense constructions restrict the passage of air. In contrast, loose knits and open meshes permit high velocity transmission. The boundary of the test stops being reliable when the pressure drop cannot be maintained across open structures.
Structural Correlation
Finishing treatments modify yarn spacing and change the porosity. Mechanical processes such as calendering flatten the yarns to compress the pore openings and decrease the transmission rate. Chemical coatings fill the interstitial gaps to block air passage entirely.
