Bathtub Materials: Acrylic, Enameled Steel, Cast Iron and Stone Resin

The material of a bathtub decides how it feels when you sit down, how heavy it is to carry upstairs, how it wears and whether a chip can be fixed. It also limits which installation types are available: cast iron freestanding tubs are common, cast iron drop-ins less so. This page compares the materials you will see in a showroom. Installation types are on our bathtub types page.

Materials side by side

No independent source measures heat retention or weight across tub materials, so the comparison below is in relative terms. Treat any precise "stays warm for X minutes" claim with caution.

Acrylic

Acrylic tubs are formed from a sheet of acrylic, then reinforced from behind with fiberglass and resin. The quality varies with the sheet thickness and the reinforcement. A well-made acrylic tub feels solid when you stand in it; a thin one flexes and can creak. Acrylic is light enough to carry up stairs and through tight hallways, which keeps installation simple, and it comes in every type: alcove, drop-in, corner, freestanding, soaking and jetted.

The color goes through the acrylic layer, so light scratches can be buffed out. Its weak point is abrasives: scouring powders and rough pads leave a haze. Most acrylic tubs are set in a mortar or foam bed underneath, which supports the bottom so it does not flex.

Fiberglass

A fiberglass tub is molded fiberglass with a thin gelcoat surface. It is the lowest-cost option and very light. The gelcoat is thinner and softer than an acrylic sheet, so it dulls, can fade and may crack if the bottom is not fully supported. In a remodel it is mostly chosen for rentals or tight budgets. Many older one-piece tub and shower units are fiberglass, and they often show their age through yellowing, a chalky surface and cracks in the floor.

Enameled steel

Enameled steel tubs are pressed from sheet steel and coated with porcelain enamel fired at high heat. The surface is hard and glossy and resists most chemicals. The steel is thin, so the tub can sound hollow and feels cold to begin with; some models have a sound-deadening coating underneath. Enamel chips if something heavy is dropped on it, and a chip can rust at the edge if it is left. Enameled steel is mostly found in standard alcove sizes at lower prices.

Enameled cast iron

Cast iron tubs are poured iron with a thick porcelain enamel surface. They are the heavy, durable tubs found in older homes, and many from the early 20th century are still in use. The enamel holds a deep gloss and resists most cleaners. Iron is cold when you first sit down but, once warmed by the water, it changes temperature slowly.

The trade-off is weight. A cast iron tub is much heavier than an acrylic one. It takes a crew to move, and for a freestanding or second-floor installation the floor framing should be checked. Our freestanding tubs page covers floor loads. Enameled cast iron and enameled steel fixtures are made to ASME A112.19.1/CSA B45.2.

Stone resin and solid surface

Stone resin tubs are cast from crushed stone, such as ground limestone, bound in resin. The color goes all the way through, and the usual finish is a soft matte. They feel warm and smooth and are mostly sold as freestanding tubs with thick, sculpted walls. Because the material is solid, light scratches and even small chips can be sanded out and refinished. Stone resin tubs are heavy, and they sit at the higher end of the price range.

Cultured marble

Cultured marble is cast from marble dust and resin with a clear or colored gelcoat surface. It is used for one-piece tubs, shower surrounds and vanity tops. The gelcoat is what protects it; once that is worn through, the material underneath stains. More on this material is in our blog post on cultured marble.

Standards to look for on the spec sheet

Standards do not tell you which material is better. They tell you a tub was made and tested to an agreed baseline, so check that the spec sheet names one.

• ASME A112.19.1/CSA B45.2 covers enameled cast iron and enameled steel tubs, sinks and shower bases (current edition 2024).
• CSA B45.5/IAPMO Z124 covers plastic fixtures, including acrylic and fiberglass tubs and tub-shower units (latest edition found, 2022).
• ASME A112.19.7/CSA B45.10 covers whirlpool and air-jetted tubs with a circulation pump, whatever the shell material.
• IAPMO/ANSI Z124.8 covers plastic liners installed over existing tubs and shower bases. A liner is not a new tub; see our page on one-day baths and liners.

What to check before you buy

1. The standard named on the spec sheet.
2. For acrylic: sheet thickness and how the tub is reinforced. Press on the floor of a display model.
3. For heavy materials: the weight on the spec sheet, the route into the room, and whether the floor framing needs to be checked.
4. The cleaning products the manufacturer allows, and what voids the finish warranty.
5. Whether the tub needs a mortar or foam bed underneath and who supplies it.
6. What the warranty covers (shell, finish, jets) and for how long, in writing.

Who should choose which

• Most hall and family baths: a well-made acrylic alcove tub. Light, warm, repairable and available in every size.
• An older home where the tub is a feature: enameled cast iron, original or new, after a check of the floor.
• A primary bath freestanding soaker: stone resin for a matte, sculpted look, or acrylic for lighter weight and lower cost.
• A rental or tight budget: enameled steel or fiberglass, accepting a shorter-feeling finish.
• A jetted tub: acrylic is the usual shell; see soaking, whirlpool and air tubs.

If you are still deciding whether the room needs a tub at all, read should you keep a bathtub. When you are ready to choose, JDI Construction's designers bring material samples to the plan and check the floor before a heavy tub is ordered. Start with bathroom remodeling in Vancouver, WA.