How C.I.S. Works With Ceramic Wrap Insulation
  As an alternative to the poured insulation, manufactures of metal chimney liners offer a ceramic wrap insulation. When a ceramic blanket is used to insulate the chimney liner, the ceramic blanket is wrapped and taped to the metal liner before the chimney liner is lowered into the chimney from the top. As the metal liner is being lowered into the chimney, the chimney liner flexes, oftentimes, tearing the ceramic blanket insulation. Protruding mortar, brick, and other rough surfaces in the interior of the chimney can also tear the ceramic blanket. If a tear in the insulation is at a point on the liner where the liner is in contact with the inside surface of the chimney, or where a flue liner is fractured, dangerous levels of heat radiation can occur from the chimney liner through the chimney to the surrounding framing.

As illustration # 6 reveals, the C.I.S. spacers, which are attached to the wrapped chimney liner before the liner is lowered into the chimney, ensure that the liner does not come in contact with the interior surfaces of the chimney. The resulting air space created by the C.I.S. spacers is a highly efficient insulating barrier that decreases the severity of the heat transfer from the chimney liner to and through the chimney walls.