Consists of a thermoplastic membrane integrally bonded to a proprietary Active Polymer Core (APC) layer. Combined with fully welded seams, this provides the ultimate waterproofing protection. This is similar to synthetic rubber, but the seams are typically heat-fused (welded) to form a continuous membrane. The 'lap' seams can also be fused with solvents instead of heat, and can be as strong as the rest of the membrane. One of the properties of thermoplastic membranes is that the material temporarily changes from a solid to a semi-solid state when heated sufficiently, enabling the sheets or panels that are overlapped to be fused together and return to a solid upon cooling. Thus, a monolithic, continuous sheet membrane is created.