US Patent 7179761 Vapor barrier

A bituminous water vapor retarder is disclosed of the type which can be used under concrete slabs in contact with soil or granular fill. The vapor barrier is a multi-ply weather coated permanently bonded semi-flexible bituminous core board composed of the homogeneous high melt point bituminous material in combination with an exclusive core suspended midpoint in the board. This core is sealed under heat and pressure between liners of asphalt and impregnated felt and a glass mat liner. An asphalt weather coat is applied to the glass mat liner and covered with a polyethylene anti-stick sheet.