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 degrees 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.