Acrylic: These tubs use fiberglass sheets that reinforce the formed sheets of colored acrylic that are over the top. They come in a large selection of colors, shapes, and sizes and are very light and easy to install. Acrylic tends to fade and scratch less over the course of time compared to their fiberglass counterparts, but it still tends to stretch over time much like a fiberglass tub.
Enameled Steel: Also Called Porcelain on steel, these tubs are made by coating a sheet of steel with a layer of porcelain enamel that make the tub durable and easy to clean. The layer of porcelain enamel is resistant to stains and most common household chemicals, and it tends to retain its gloss for a long time. Enameled steel tubs are heavier and the steel can rust if the coating chips.
Cast Iron: These are made by pouring molten iron into a form and then coated with a thick layer of enamel. Resistant to Scratching, denting, chipping, as well as most household cleaners, its beauty is sure to last a lifetime. Cast iron tubs come in a variety of shapes and colors - they seem to have a richness that other materials do not provide. Cast iron also provides excellent water heat retention. On the down side they are extremely heavy, and may cause you to add extra support to your floors. These are also among the most expensive tubs.