Cast Iron bathtubs are produced using molten iron poured into a mold. Kohler is the only remaining U.S. manufacturer of cast iron bathtubs. They are very expensive to produce, and are perceived as the ultimate in quality, durability and performance. Their disadvantage is their weight, whichmake them difficult to install. The surface is coated with porcelain in the color desired. Multi-Tech Products produces a kit to repair porcelain enamel. Cast iron bathtubs are also manufactured in China.