Two standard variations of ceramic insulation for box furnaces are rigid ceramic fiber boards and flexible blankets. They are manufactured using strands of refractory silicate compressed or woven into a lightweight textile, with excellent inherent strength and low thermal conductivity. Ceramic fiber board is often used as a secondary form of insulation in box furnaces to support the performance of flat plate heaters. As an alternative, a flat plate heater — a composite heating element and insulation product — can be supplied that exploits the low thermal mass of ceramic insulation to optimize the radiation of heat through a processing chamber. This utilizes a cast plate ceramic with grooves designed to house wire heaters, which may be fully embedded or partially exposed. Typical heating elements include helical coils, rod overbend and ribbon heaters.