FlexSeal™ Caulk Grade Sealant is a white solvent-based synthetic elastomeric sealant. 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™ CaulkGrade Sealant is especially suited for use in any application where caulk is typically used.