Selkirk Corporation SPR8L36P 8 Inch x 36 Inch Superpro Factory-Built Chimney Length 304-alloy Inner And Outer Walls SuperPro features 304-alloy stainless steel for both its inner and outer walls. The mineral wool insulation is formulated for optimum performance while dramatically reducing chemically active ingredients. It provides a thermal delay that resists and contains surges of heat keeping the outer liner cooler. SuperPro couplers are embossed which reduces moisture penetration increasing longevity of the chimney. Inside diameter 8 inches - length 36 inches.