A Test Method to Determine the Relative Humidity Dependence of the Air Permeability of Woven Textile Fabrics

This paper describes a test method used to determine the relative humidity dependence of the air permeability of hygroscopic woven textile fabrics. Changes in fabric structure as hygroscopic fibers swell at high humidities can have a large influence on the measured air permeability of materials such as cotton, wool, silk, and nylon fabrics. The method is sensitive enough to show sorption hysteresis effects in the relative humidity versus air permeability curve. The instrumentation also permits dynamic measurements during a step change in relative humidity. Typical results are shown for seven fabrics, covering a range of fiber hygroscopic properties and air permeabilities.