Plenum Cables are formulated to particularly high fire retardant specifications to withstand the severity of ventilation or wind tunnel effects in building fire situations. It is required in plenum areas because of fire regulations. It is coated with a nonflammable material, often Teflon or Kynar, and do not give off toxic fumes if they catch fire. It uses insulation and sometimes jacketing made with fluorocarbon plastics for their smoke and flame-retardant properties. It can be openly routed in plenums without any restrictions. It is certified for installation in air ducts and open spaces over suspended ceiling without conduit. It is also used for cable runs through a return air system.