A heater element (41) includes a first polymer film (42) having an electrically conductive circuit. The circuit may include conductive ink (44), a second polymer film (43), and/or resistive or conductive overmolded material (57). The first polymer film (42) is molded into at least one surface of a molded object (46, 50, 51, 150, 250, 350). The molded object may be a humidifier (51) or a component (50, 150, 250, 350) of a humidifier. A method of manufacturing an in-mold heater element (41) includes providing an electrically conductive circuit on a surface of a first polymer film (42); placing the first polymer film including the electrically conductive circuit in a mold such that the non-printed surface of the polymer film is adjacent the mold; and insert molding resin (46) to form a predetermined molded shape such that the first polymer film (42) is incorporated within at least one surface of the molded shape. A method of humidifying a flow of pressurized breathable gas includes passing the flow of pressurized breathable gas over a supply of water (W) contained in a tub (50, 150, 250, 350). The tub is formed of molded resin and a heater comprising a polymer film (42) having a layer of electrically conductive ink (44), a stamped resistive or conductive film (43), and/or resistive or conductive overmolded material (57) on a first surface is molded at least partially within the resin.