Shop for Heating, Venting & Cooling at The Home Depot. DuraPlus is designed to stay cool on the outside, to provide a hot draft on the inside, to boost stove efficiency, and to provide for a fire-safe design that protects both the chimney and the building. This triple-wall chimney features two insulating layers (ceramic blanket, plus air space). The ceramic blanket insulation is held securely in position, eliminating hot spots common with loose-fill type insulations. In the event of a creosote fire, the compressible blanket insulation permits the chimney liner to expand outwardly in a radial direction. Designed for normal, continuous operation at 1000 degree F flue gas temperatures, DuraPlus is subjected to rigorous and stringent HT requirements of the UL standard, including one hour at 1400 degrees F, plus three ten minute chimney fire tests at 2100 degrees F.