GAF TopCoat FlexSeal Caulk Grade is a white solvent-based synthetic elastomeric sealant for detail work on TPO and PVC. FlexSeal is extremely flexible and durable, but with a higher viscosity formulation than Standard FlexSeal. Like all solvent-based products, the surface must be clean, completely free of moisture and residual contaminants before application. FlexSeal Caulk Grade is especially suited for use in any application where caulk is typically used. If a more fluid viscosity is desired, FlexSeal is also available in both a standard viscosity as FlexSeal and a low viscosity version FlexSeal LV.