one end 46 of cable 20 substrate 50 is skived to expose the surfaces of wires 42 44 which are then attached to two tin plated and presoldered copper tabs 47 49 the tabs are in turn connected to the heating element at junction 38 using conductive adhesive so that tab 47 makes electrical contact with heater conductive stripe 36 and tab 49 with stripe 34 at the other end 78 of cable 20 substrate 50 is similarly skived and cable 20 is attached to plug 18 by soldering so that wires 42 44 respectively make electrical contact with two metal conductors 150 152 on plug 18 conductors 150 152 are small strips of metal e g presoldered tin plated copper foil that are glued to plug 18 conductor 152 folds over and lies on both faces of the plug as does conductor 154 when the plug is inserted into a cigarette lighter socket conductor 150 touches the metal wall of the inside of the lighter socket and the leading tip of conductor 152 touches the central contact of the socket plug 18 includes a biodegradable paper substrate 54 laminated on both sides with plastic layers 55 57 one end 56 of plug 18 has a width w approximately the size of in particular slightly greater than the inside diameter of the cigarette lighter socket the leading end 58 of plug 18 has tapered edges 60 62 to make the plug easier to insert.