Percy's SEAL-4-GOOD Reusable Flange Gaskets are multi-layered and made from a special "Dead Soft" aluminum, which conforms to header flanges for the ultimate seal. Because the SEAL-4-GOOD is made from multiple layers of dead soft metal, it easily conforms to small imperfections that a copper gasket simply can not. Because of this construction, these gaskets will not blow out or burn out when properly installed.