diffusion de la vapeur d'eau

OBS: vapor diffusion. The movement of water vapor between two areas caused by a difference in vapor pressure, independent of air movement. The rate of diffusion is determined by 1) the difference in vapor pressure, 2) the distance the vapor must travel, and 3) the permeability of the material to water vapor. Hence, the selection of materials of low permeability for use as vapor retarders in buildings.