Plenum

[Also known as Plenum-Rated] A type of cable jacket with fire-rated properties typically made of Teflon or Teflon derivatives. The building codes in most localities require the use of fire-rated cables when they are run through the plenum spaces of a building to prevent the spread of fire or the release of toxic gases that can result from the burning of standard PVC materials. The plenum space is typically the open space between a drop ceiling and the roof, or the open space inside walls, for which the cable gets its name.