Membranes of various types are often used in the construction industry for the exterior and interior of the building makeup, we sell variety of these. For example, breather membranes are water resistant but vapour permeable and are typically used externally. A vapour barrier (Vapour Control Layer VCL) is positioned on the warm side of the structure and prevents the warm moist air from penetrating and condense as water which could cause mould growth and other such issues.