A vapor barrier is a layer designed to trap moisture and water. It is mainly used for roof extensions or roof insulation. For this purpose, the vapor barrier is mounted on the insulation material, i.e. it is attached to the inside of the insulation. A vapor barrier must meet the requirements of DIN 4108-4 in order to be designated as such. For example, such a barrier must have an sd value (diffusion-equivalent air layer thickness) that is above 1,500 m. In contrast, a vapor barrier is a diffusion-inhibiting layer with an sd value between 0.5 and 1,500 m. This value shows how long it takes for water vapor to pass through a vapor barrier or vapor retarder. It therefore indicates how many meters water vapour can travel through a layer of air. Materials such as PE film, aluminum foil or plasterboard composite panels are used for vapor barriers.
