The invention relates to a method of making a part (2) of thermoplastic material covered on the surface by an electrically conductive foil (4) of thickness less than 0.1 mm, the part also including a rib (6), and the method comprising a step of depositing on an inside surface of a mold defining the shape of the part (2), an electrically conductive foil (4) in such a manner as to cover at least part of a blind orifice of the mold opening out into its inside surface and defining the shape of the rib (6), a step of forming at least one opening (14) through the foil (4) leading to the orifice and shaped to allow the fluid thermoplastic material to pass therethrough, and to ensure that the foil (4) remains in a single piece, and a step of filling the mold with fluid thermoplastic material.