I've always thought "Luan" was the term for plywood. It's a smooth surface on both sides with no knots or fillers. The exterior walls are fiber galss coated Luan. Some are gelcoat (smooth & shiny) and some are a slightly textured fiberglass surface. The interior Luan walls are coated with wallpaper/vinyl material to give it a "painted" appearance. Both the exterior and interior walls are laminated to the aluminum frame with styrofoam insulation in between.