The building contains over 44,000 U.S. tons (40,000 metric tons) of structural steel, and almost an acre of office space per floor. The U.S. Steel Tower is architecturally noted for its triangular shape with indented corners. The building also made history by being the first to use liquid-filled fireproofed columns. U.S. Steel deliberately placed the massive steel columns on the exterior of the building to showcase a new product called Cor-ten steel. Cor-ten resists the corrosive effects of rain, snow, ice, fog, and other meteorological conditions by forming a coating of dark brown oxidation over the metal, which inhibits deeper penetration and doesn't need painting and costly rust-prevention maintenance over the years. The initial weathering of the material resulted in a discoloration of the surrounding city sidewalks, as well as other nearby buildings. A cleanup effort was orchestrated by the corporation once weathering was complete to undo this damage, but the sidewalks still have a rusty tinge. The Cor-Ten steel for the building was made at the former U.S. Steel Homestead Works.