... air heating, heating a surfaceCeramic shellCeramic shell, with wire and ceramic insulationLow cost, small bulk, insulating shellNot ... very small bulk, low powerPlastic shellPlastic shell, with wire and plastic insulationLow cost, small bulk, insulating shellNot ... can insert on a circuit boardResin coating shellResincoating, with wire,resin insulationLow cost, small bulk, insulating shellVery ...