Air and Water Permeability Testing

Air and water permeability testing measures the volumetric flow of air or liquid through fabric under defined pressure differentials — functional properties critical for filtration efficiency, breathability, rainwear waterproofness, and technical fabric hydraulic performance. Air permeability (ISO 9237, SDL Atlas M021S, TEXTEST FX3300, 20 cm² test head area, 100 Pa differential, air flow in L/m²/s or cfm/ft²): woven cotton shirting 150–400 L/m²/s; PVC-coated architectural membrane <1 L/m²/s; air-slide fabric (fluidisation conveying belt) 50–500 L/m²/s; geotextile needle-punched nonwoven 80–120 L/m²/s (MARV value ISO 11058). Water permeability of geotextiles (ISO 11058, permittivity ψ = q / A × h where q = flow rate m³/s, A = area m², h = hydraulic head m — unit s⁻¹): separation geotextile permittivity ≥ 0.02 s⁻¹; drainage geotextile ≥ 0.10 s⁻¹; filtration geotextile 0.05–0.20 s⁻¹. Hydrostatic pressure resistance (ISO 811, water column rise 100 mm/min, reading at first 3 droplets penetrating fabric: waterproof apparel shell ≥ 10,000 mm H₂O; breathable membrane outer shell ≥ 20,000 mm; submersible drysuit ≥ 100,000 mm). Air permeability standards differences: ASTM D737 uses 12.7 mm H₂O (125 Pa) differential, 38.3 cm² test area — not directly comparable to ISO 9237 at 100 Pa, 20 cm². Filtration efficiency (ASTM F2299, EN 14683, particle challenge test, sodium chloride aerosol or polydisperse latex particles): surgical mask BFE (Bacterial Filtration Efficiency) ≥ 95%; N95 respirator PFE (Particulate Filtration Efficiency) ≥ 95% at 0.3 µm; HEPA filter ≥ 99.97% at 0.3 µm (IEST-RP-CC001).