For use with the Simpson DuraFlex Zero Clearance Insulation Sleeve to meet the UL1777 standard for masonry chimneys and wood burning appliances. DuraFlex SS – Ensures safe and efficient venting of heating appliances while protecting the masonry chimney from the damaging effects of flue product condensation. The 316Ti SS is designed for use with wood-burning wood pellet and non-condensing gas coal and oil appliances. Titanium is designed for harsher conditions for more resistance to corrosion such as coal. Measures 6in diameter x 20ft.