Thermal insulation is usually incorporated in the spaces between the studs of external walls and protective membrane materials may also be required, depending on the design of the wall. For most external walls a breather membrane on the external face of the panels protects the panels during construction and provides a second line of defense against any wind-driven rain that may penetrate the completed external cladding.
A vapor control layer in the form of polythene sheet or plasterboard with an integral vapor control layer is normally required on the 'warm' side of the insulation, behind the plasterboard lining to limit the amount of water vapor entering the wall panel.