Abstract: Electrically conductive honeycomb structures are provided which include an inlet face, an outlet face, a set of short insulating slots extending from the inlet face towards the outlet face, and a set of long insulating slots extending from the outlet face towards the inlet face. The short and long slots are interdigitated so that electrical current flowing parallel to the inlet face must follow a serpentine path around the ends of the slots. The serpentine path is located closer to the inlet face than to the outlet face so that the heating effect of the current is localized near the inlet face.