Part I: Method of Measurement

Methods employed in the measurement of permeability to water vapor of materials offering high resistance are unsuited for use with textile fabrics. The problem of meas urement is reviewed, and it is pointed out that the relationship between the diffusion resistance and the thickness of a fabric is linear but not proportional. A method de veloped particularly for low-resistance laminae is described and validated, noting the existence and importance of air layers external to the lamina. It is shown quantitatively that the resistance of these layers is reduced by air movement.