DuraFlex SS and DuraFlex AL Relining Systems ensure safe and efficient venting of heating appliances while protecting the masonry chimney from the damaging effects of flue product condensation. DuraFlex SS and DuraFlex AL are listed and tested by Underwriters Laboratories and carries a Limited Lifetime Warranty. DuraFlex SS is designed for use with pellet, non-condensing gas, and oil appliances. When used with the Simpson Dura-Vent Two-Ply Insulation Sleeve, it may be used for relining wood-burning fireplace inserts and stoves to meet UL and ULC standards with 0” clearance to masonry. DuraFlex AL provides an economical means to reline masonry chimney for Category I gas furnaces, water heaters, fireplace inserts, and noncondensing boilers. DuraFlex AL is made of two-ply aluminum.