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