The document describes a weldable thermoplastic membrane with an active polymer core layer for waterproofing foundations. The core layer is self-sealing and bonds to concrete to enhance puncture resistance. The membrane features a knitted polyester fabric coated with thermoplastic and an adhesive layer. It is produced with DuPont Elvaloy KEE plasticizer to maintain flexibility and prevent cracking over time. The membrane provides a waterproof and puncture-resistant barrier when installed on foundations, with welded seams forming a monolithic barrier and the active core layer stopping leaks from migrating through any defects in concrete.