A method for inflating a chamber in an article composed at least partially of polymer layers, such as thermoplastic layers. The method can allow for forming an aperture in a polymer layer, inflating a chamber or volume in fluid communication with the aperture, and then welding or sealing the chamber so that the inflation fluid is substantially retained in the chamber and/or does not escape via the aperture. In various aspects, the formation of the aperture, inflation of the chamber, and sealing of the chamber 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 with a cupped surface that allows the top layer of a thermoplastic article to be breached without forming a hole in at least one lower layer.