Three types of humidity-variable vapor retarder were focused and their water vapor transmission properties in the directions from hydrophilic layer to hydrophobic layer and vice versa were measured by cup method. Eight different relative humidity conditions in test cup were controlled by desiccants, aqueous solutions, or water. In the high relative humidity range, the vapor transmission resistances were positively small for all three films and in both directions. In the low relative humidity range, however, the resistances were enough high in one direction but mildly low in the other direction. Furthermore, the resistances measured by desiccants and those by aqueous solutions had an opposite trend, that indicated that the dry cup method with desiccants should not be used for humidity-variable film with hydrophilic layer.
