Etched Foil PI flexible heaters are made with a thin metal foil (.001"), usually a nickel base alloy, as the resistance element. The resistance pattern to be etched is designed in CAD and transferred to the foil, which is laminated to the insulating substrate. The element/substrate is then processed through an acid spray to produce the desired resistance pattern. The top layer is then added and laminated. Lead wires are attached to the heater and insulated with epoxy cement to complete the heater.