A top quality stainless steel, high temperature insulated twin wall flue pipe, guaranteed for 10 years against defects due to faulty manufacture. This stainless steel system consists of a 25mm high density insulated core surrounded by 316 grade inner liner is 0.5mm thick, (25% thicker than some products) and the 304 grade outer casing is 0.5mm thick. They are BSRIA approved to BS4543 Parts 2 & 3 and HETAS approved for solid fuel burning. It is supplied with a bright Annealed Mirror Finish. IMPORTANT: Your stove must have a minimum of a 1 metre vitreous flue pipe between the stove and the stainless steel twin wall system.