The air permeability of textiles used in clothing is of particular importance in the functional clothing and technical products sectors (e.g. parachutes). In fabrics, the permeability can significantly affect how the human body is able to regulate moisture and temperature. In the case of parachutes, an air permeability test provides important information about its suitability for use. We measure the flow speed of the air that penetrates a defined area of the fabric at a specified differential pressure in accordance with EN ISO 9237.