Stainless Steel Flexible Chimney Flue Liner. Flexible metal acid resistant steel used where cannot be used straight element chimney liner. This multi-fuel flexible fuel liner is heats approved and suitable for lining existing chimneys. Having a flexible flue liner will help the efficiency of your stove and also the way fuel burns as well. It is also highly recommended especially if you have cracks and leaks in your existing chimney. Thickness 0.12mm (DN500). Sort of Material – Steel, type 1.4404 (316 grade). Temperature Level – T450. Gas Tightness(pressure class) – N1 (40Pa). Condensate penetration resistance – W. Durability against corrosion – Vm. Soot fire resistance – G.