Stainless steel outer casing and inner liner. Double-wall pipe with solid pack insulation. Tested to withstand 2100 F (degree Fahrenheit). UL (Underwriters' Laboratories) listed. This test helps to prevent product damage or structural hazard during brief periods of this excessive chimney temperature. Normal temperature is 1000 F. Pipe Data: Minimum clearance to combustibles - 2". Stainless steel thickness: Inner lining and outer casing - .012"; couplers - .016". Insulation density - 23 lb/cu ft (pounds per cubic foot). Insulated pipe lengths are furnished with a Locking Band (preassembled with captured nut and screw).