..., for example, because such perfect seal is only realizable for a sample larger than the cup mouth, an edge correction must be applied to the value measured. As far as direction is concerned, measurements on a couple of hygroscopic materials gave different vapor permeability results for inward and outward flows...

... for Water Vapor Transmission of Materials (E 96), is widely used in North America and other parts of the world for this purpose. Recently the latest ASTM standard (E 96/E 96M–05) has started taking into account various corrections (e.g., buoyancy correction, correction for resistance due to still air...