Perm-A-Barrier VPS (Vapor Permeable Sheet) is a self-adhering vapor permeable air barrier membrane consisting of a breathable carrier film with a specially designed adhesive. Perm-A-Barrier VPS provides superior protection against the damaging effects of air and water ingress on building structures. As a vapor permeable membrane, Perm-A-Barrier VPS permits the diffusion of water vapor that may otherwise condense in the wall structure; but is impermeable to liquid water, which allows the material to act as a water drainage plain. Perm-A-Barrier VPS is vapor permeable for wall assemblies requiring this breathable characteristic.