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 2-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°F flue gas temperatures, DuraPlus is subjected to rigorous and stringent HT requirements of the UL standard, including 1-hour at 1400°F, plus three 10-minute chimney fire tests at 2100°F.