Stainless steel chimney liners, either rigid or flexible, are used to repair or replace an existing chimney flue that has been compromised. It is commonly used inside a masonry chimney when the clay tiles have cracked or mortar joints have deteriorated. Stainless steel liners are also used in masonry chimneys that were built without flue tiles. Stainless Steel is the best material for the application so most liners come with a lifetime warranty.