This document specifies a method for determining the water-vapour transmission properties of coatings of paints, varnishes and related products. It supplements ISO 12572. As far as possible, the procedure, the definitions and the calculations have been taken over from ISO 12572. ISO 12572 can be consulted, if necessary, to obtain a better understanding of the procedure specified in this document. Water-vapour transmission rates of more than 680 g/(m2Å"d) (i.e. water-vapour diffusion-equivalent air layer thicknesses, sd, of less than 0,03 m) are not accurately quantified by the test method described in this document.