This 7 inch (180mm) 316 grade flue liner is one of the strongest and most reliable flue liners on the market. As the liner is constructed from two individual strips of 316 stainless steel, where as most other liners on the market are made from one strip of steel which is folded to create the inner and outer layer. This folding weakens the steel. As Dura Flue is made from two strips of steel this weakening doesn’t happen meaning it’s a strong more reliable flexible flue liner. It also has a 15 year guarantee compared to the 10 years that most other liners offer.