Thermoplastic materials, such as polyvinylchoride, cannot normally be heat bonded to certain higher-melting synthetic fabrics, such as nylon or the like, which are of the densely woven type and are also frequently treated with silicone or analogous substances to make them water repellant and/or windproof. The present method overcomes this problem by heat-bonding such materials under pressure and the application of a dielectric field, and by causing sufficient dielectric resistance to be present at the synthetic fabric so that the dielectric field is able to heat the synthetic fabric to a temperature at which it becomes sufficiently flowable to bond with the thermoplastic material.