Water Vapor Permeability of Barrier Foils

ProUmid Application Note

Moisture control and management are important in building construction and planning. Depending on their properties, materials such as plasters or paints can help to regulate the indoor climate or protect facades from the effects of moisture and weathering. Also, special vapor barriers and vapor retarders play an important role in protecting buildings against harmful effects of moisture. These are used specifically on exterior walls and roof structures and are intended to protect the building components from waterlogging, which tends to occur at cold thermal bridges.

The term vapor retarder refers to a film system that allows diffusion in both directions. The amount depends on the film properties, expressed by the sd-value. Such films are therefore able to transport moisture in the direction of the concentration gradient. A vapor barrier, in contrast, is vapor tight. This means that the moisture transport through the film is suppressed so that the moisture remains in the building.

Application Note

So-called moisture-adaptive vapor retarders are more recent developments in the field of moisture protection for buildings. With this type of foil system, the water vapor permeability adapts to the prevailing moisture conditions. If large amounts of moisture are present, the diffusion resistance increases, preventing large amounts of moisture from penetrating.

An optimized insulation system is therefore essential both for protecting a building and for ensuring a pleasant indoor climate, preventing waterlogging and mold growth.

This application note shows the use of permeability measurements to characterize water vapor insulating films used in building constructions.