Fiberglass tubs and showers are surfaced with either acrylic plastic or gel coat resin. So this is a laminate product. Unlike metal, fiberglass is not only used to make soaker tubs, but also jetted tubs, showers, and tub/wall combination units. There are even sinks made of fiberglass reinforced acrylic. But it is debatable whether the soft acrylic provides a durable enough wearing surface for the more demanding use sinks receive. Especially for kitchen use.

There are some good advantages to fiberglass tubs over metal tubs. They can be fabricated in many shapes and styles to enhance comfort and luxury. Even two person tubs are available. They come with more comfortable lumbar support and deeper water depth. Often arm rests and grab bars are built into them. They are by design, warmer to the touch. Metal transmits heat more easily. A tub installation trick is to stuff fiberglass pink insulation around tubs to save on hot water costs.

As a guide, acrylic is used primarily on soaker tubs, jetted tubs, and showers and tub/wall units that have a dome (I.e. enclosed at the top). Gel coat is used mostly on showers and tub/wall units that do not have domes.

To build a fiberglass tub, a mold is fabricated of the design. If manufacturing gel coat units, the gel coat, basically a colored resin, is sprayed on first to make the finished surface. Then the fiberglass reinforced backing is sprayed on with what is called a chopper gun. A chopper gun sprays a mixture of the cloth strands and resin which provides strength and rigidity. If building acrylic units, the manufacturer purchases cast acrylic sheeting from chemical divisions of large companies like Mitsubishi, Dupont, Aristec, etc. So acrylic tubs basically start their lives flat. Acrylic is a thermal plastic which means it becomes pliable when heated. The sheets are thermally formed over a mold of the tub in a large oven. There are small holes in the mold where a vacuum draws the acrylic tight to the mold. Once cooled, the acrylic is removed from the mold and the chopper gun is used to apply the fiberglass reinforcing on the back.