This extended width wall sleeve is fully insulated and made of galvanized steel. it is welded and protected with baked-on enamel. Welded areas are protected with a sealing compound to prevent rust. 5304483759 — Metal Wall Sleeve Extension, Insulated, 16" 5308815304 — Metal Wall Sleeve Extension, Insulated, 18" 5308815305 — Metal Wall Sleeve Extension, Insulated, 24" 5304483760 — Metal Wall Sleeve 3" Adapter