6" DuraVent DuraPlus Attic Insulation Shield 6DP-IS This attic insulation shield is required for installations that pass through an attic to prevent insulation and debris from accumulating near the chimney. Fits over firestop radiation shield or a support box. Consists of two parts: a collar and a base. Use when air-cooled chimney is required Free-floating inner 430-alloy liner maintains structural integrity in chimney fires 2" clearance to combustibles Outer diameter is 4" larger than inner diameter Triple-wall chimney For uses with wood stoves fireplaces furnaces boilers stoves ranges water heaters or other appliances fueled by wood oil coal or gas Clean smooth exterior finish .016” 430 stainless steel outer wall or .018” galvanized steel outer wall. .018” aluminized steel intermediate liner. .016” 430 stainless steel inner liner. Insulated layers plus ventilated air space. Locks tightly with a precision twist-lock connection.