fills the gap between the home and the siding. Products provide environmental advantages by reducing energy use by up to 20 percent. On average, insulated siding products have an R-value of 3.96, triple that of other exterior cladding materials. Insulated siding products are typically Energy Star qualified, engineered in compliance with environmental standards set by the U.S. Department of Energy and the United States Environmental Protection Agency. In addition to reducing energy consumption, insulated siding is a durable exterior product, designed to last more than 50 years, according to manufacturers. The foam provides rigidity for a more ding- and wind-resistant siding, maintaining a quality look for the life of the products. The foam backing also creates straighter lines when hung, providing a look more like that of wood siding, while remaining low maintenance. Manufacturers report that insulated siding is permeable or "breathable", allowing water vapor to escape, which can protect against rot, mold and mildew, and help maintain healthy indoor air quality. Metal siding Metal siding comes in a variety of metals, styles, and colors. It is most often associated with modern, industrial, and retro buildings. Utilitarian buildings often use corrugated galvanized steel sheet siding or cladding, which often has a coloured vinyl finish. Corrugated aluminium cladding is also common where a more durable finish is required, while also being lightweight for easy shaping and installing making it a popular metal siding choice. Formerly, imitation wood clapboard was made of aluminium (aluminium siding). That role is typically played by vinyl siding today. Aluminium siding is ideal for homes in coastal areas with much moisture and salt, since aluminium reacts with air to form aluminium oxide, an extremely hard coating that seals the aluminium surface from further degradation. In contrast, steel forms rust, which can weaken the structure of the material, and corrosion-resistant coatings for steel, such as zinc, sometimes fail around the edges as years pass. However, an advantage of steel siding can be its dent-resistance, which is excellent for regions with severe storms—especially if the area is prone to hail. The first architectural application of aluminium was the mounting of a small grounding cap on the Washington Monument in 1884. Sheet-iron or steel clapboard siding units had been patented in 1903, and Sears, Roebuck & Company had been offering embossed steel siding in stone and brick patterns in their catalogues for several years by the 1930s. Alcoa began promoting