A tool for inflating a chamber (50) in an article composed at least partially of polymer layers, such as thermoplastic layers. The tool can allow for forming an aperture in a polymer layer (350), inflating a chamber (50) or volume (130) in fluid communication with the aperture, and then welding or sealing the chamber (50) so that the inflation fluid is substantially retained in the chamber (50) and/or does not escape via the aperture. In various aspects, the formation of the aperture, inflation of the chamber (50), and sealing of the chamber (50) or aperture can be performed by a single tool and/or based on a single registration of the thermoplastic article with a tool. In some aspects, formation of the aperture is enabled in part by using a punch (100, 201, 205) with a cupped surface (341) that allows the top layer of a thermoplastic article to be breached without forming a hole in at least one lower layer (350).