DuraFlex 304 and 316 are lighter, more economical liners. Excellent when there are minimal offsets in the chimney. DuraFlex 304SS and 316SS are intended for wood burning, non-condensing gas and oil fired appliances. Where greater corrosion resistance is desired, such as coal-fired appliances, DuraFlex 316 is recommended. DuraFlex 304SS and 316SS are listed to UL 1777 and ULC S635.