Abstract

The standard method ISO 14268 describes a technique for the measurement of water vapour permeability (WVP) of leather which is based on the mass surge of a desiccant contained in a vessel sealed with the specimen under test. The water vapour that seeps inside the container through the leather specimen is absorbed by the desiccant, the mass of which increases proportionally; fresh water vapour is provided onto the external side by a constant flow of air conditioned at 23°C and 50% relative humidity that is perpendicularly conveyed onto the specimen surface by a rotating fan. Since the inner side of the vessel is kept dry by the desiccant, the difference of chemical potential between the two facets generates a diffusive force (quantitatively accounted for by the first Fick’s law) that drives water vapour across the leather piece in the outin direction. The mass increase of the desiccant nominally equates the total amount of vapour that has crossed the leather specimen so that the WVP can be calculated by dividing the mass growth of the desiccant by the duration of the measurement (between 7 and 16 hours) and by the exposed area of the specimen.