Simpson Duravent 4DFA-35K 4" DuraFlex AL Flexible Liner Type B Gas Vent Aluminum Kit includes: DuraFlex AL 35 foot length., DuraFlex AL Cap, DuraFlex Top Plate, and DuraFlex Mortar Sleeve. Protects the masonry chimney from damaging effects of flue product condensation. Design is stylish and innovative. Satisfaction Ensured. Dimensions: 4" x 35'.