Perform one of the following test methods on the material assembly. It is not necessary to evaluate the air permeability of individual layers in a multi-layer assembly.
1. EN 14683 (Annex C) using 8 L/min air flow, with standard diameter of 25 mm. 2. ASTM D737 using a standard 125 Pa pressure drop. Use the standard 38.3 cm2 test area. 3. ISO 9237 using a standard 100Pa pressure differential
The following air permeability values are recommended for face coverings: For EN 14683 (Annex C), a maximum of 36.7 Pa/cm2. For ASTM D737, a minimum of 37.5 ft3/min/ft2 (1.14 L/min/cm2). For ISO 9237, a minimum of 0.91 l/min/cm2 (or 15 cm/s).
Test additional specimens after multiple laundering cycles (see Laundering and Care Considerations). Do not retest the same specimens.
Air permeability is measured on the fabric only. While this test indicates the potential for the fabric to be effectively used in a face covering, construction, printing, and other processes may also impact the breathing resistance of the finished face covering.