Bathtub Types: Acrylic, Cast Iron, Steel, Engineered Stone
Acrylic, cast iron, steel and engineered stone bathtubs: weight, heat retention, lifespan and price — how to choose a material when sourcing from China.
The bathtub is the heaviest, longest-lived fixture in any bathroom — unlike a faucet or showerhead, it doesn’t get swapped out every few years, and the material you pick drives the structure’s weight, the water’s heat retention, and the project’s final cost, often by a large multiple. When sourcing from China, a mistake in the material spec means either an overloaded floor slab or a tub that goes cold in ten minutes. Here are the four main materials and what to lock down in the factory contract.
Acrylic bathtubs
The most common material in the mid-range and premium segments. A sheet of acrylic is vacuum-formed into a basin, then backed with a support layer — fiberglass with polyester resin, or plain plastic in budget models.
- Pros: lightweight (25–40 kg without the frame), warm to the touch, scratches and small chips sand out on site with no need to replace the unit, moldable into virtually any geometry — corner, oval, or built-in models for a niche.
- Cons: cheap acrylic (thinner than 4–5 mm, or with no fiberglass backing) flexes under weight and eventually “drifts” — the base loses its shape. Sheet thickness and backing quality are the main things to lock down in the spec.
- What to check: the acrylic sheet thickness (from 5 mm for cast acrylic — extruded acrylic is cheaper and thinner), the backing composition (fiberglass plus resin, not a bare PVC frame), and a steel reinforcing frame under the base on larger models.
Cast iron bathtubs
A classic that hasn’t changed in decades: a cast iron basin is poured as one piece and enameled during firing.
- Pros: the longest lifespan in the category (30–50 years with careful use), the best heat retention thanks to the metal’s mass, and enamel that resists household chemicals and doesn’t scratch under normal care.
- Cons: heavy (80–120 kg empty, up to 300 kg full) — needs a solid floor and at least two installers; a limited range of shapes (mostly rectangular and oval); and once the enamel chips, the exposed metal rusts and the repair shows.
- What to check: wall thickness (3.5–5 mm — thinner risks casting deformation and louder water noise) and enamel coating thickness — thin enamel yellows and develops a network of hairline cracks within a few years.
Steel bathtubs
Stamped from a steel sheet and enameled just like cast iron, but the process and metal gauge are fundamentally different.
- Pros: lighter than cast iron (15–25 kg), cheaper than both premium options, and heats up quickly.
- Cons: cools fast (thin metal barely retains heat), rings and booms when filling without bottom sound-damping, and the enamel chips more easily on impact than cast iron’s.
- What to check: metal gauge — from 3.5 mm for a quiet, durable tub; anything under 2.3 mm is a budget option only suited to guest bathrooms. Confirm the sound-damping coating (bitumen or polymer) is applied to the underside of the base.
Engineered stone bathtubs
Cast marble or quartz composite is poured into a mold as a solid monolith, rather than formed from a sheet like acrylic.
- Pros: the most premium look in the category, holds its shape without warping from boiling water for decades, can integrate seamlessly with a countertop or platform, and chips sand out on site.
- Cons: the highest price in the category (2–4x an acrylic tub of the same size), heavy (150–250 kg), and needs a reinforced floor base plus rigging for delivery and installation.
- What to check: the pour wall thickness (from 12–15 mm for strength), the filler composition (quartz composite is stronger than cast marble), and a protective gelcoat on the working surface.
Comparison table
| Material | Weight (170 cm, empty) | Heat retention | Lifespan | Price | Where to use |
|---|---|---|---|---|---|
| Acrylic | 25–40 kg | Medium, warm to the touch | 10–20 years | $$ | Universal: apartments, rentals, HORECA |
| Cast iron | 80–120 kg | High, holds heat long | 30–50 years | $$$ | Premium homes, renovations with solid floors |
| Steel | 15–25 kg | Low, cools quickly | 10–15 years | $ | Budget projects, guest bathrooms |
| Engineered stone | 150–250 kg | High, won’t warp from boiling water | 25–40 years | $$$$ | Premium hotel rooms, platform build-ins |
What to lock down in the spec when ordering from a factory
- Material thickness — acrylic from 5 mm, cast iron from 3.5 mm, steel from 3.5 mm, stone from 12–15 mm. Without a number in the contract, the factory is free to ship the minimum allowable thickness.
- Backing type and thickness (for acrylic) or enamel thickness (for cast iron and steel) — this drives the actual lifespan, not the advertised one.
- Unit weight and floor load — critical for cast iron and stone when ordering for upper floors or light framed structures.
- Geometry and mounting dimensions — for the drain, faucet, and supports, especially on built-in and platform models.
- A sample or reference unit before the production run — enamel color, acrylic smoothness, and bubbles are only visible in person; photos won’t show the difference.
The tub is one part of a full bathroom fit-out: for faucets, see our guide on cartridges and body materials; for sinks, see sink types; and for a broader overview of sourcing bathroom fixtures from China, see sourcing bathroom fixtures from China.
Sourcing bathroom fixtures from China and want to be sure the tub can take the load and won’t go cold in ten minutes? Send us your project spec — we’ll help lock down the material, thickness, and weight in the contract, check a sample before the production run, and quote delivery to your site. Dream View’s fixed commission is 10% of the order value. Learn more on our China sourcing agent services page.
Frequently asked questions
Which holds heat better — acrylic, cast iron, or steel?
Cast iron holds heat longest thanks to its wall thickness (3–5 mm) and the metal's high heat capacity — the water cools slowly because of the sheer mass of iron. An acrylic tub with a reinforced backing comes second: the acrylic itself is thin but a poor heat conductor, so it doesn't pull warmth out of the water. Steel cools fastest — thin metal (2.3–3.5 mm) sheds heat into the air almost instantly and has almost no heat capacity of its own.
Why does a steel tub "ring" when you fill it, and is that a problem?
Ringing and booming as water fills the tub signals thin metal (under 2.3 mm) without proper sound-damping on the underside. Thickness from 3.5 mm with a bitumen or polymer coating sprayed on the bottom kills the vibration almost entirely. Ask the factory for the exact metal gauge in the spec sheet, not just the generic label "steel tub."
How much does a cast iron tub weigh, and will my floor take it?
A standard 170 cm cast iron tub weighs 80–120 kg empty and roughly 250–300 kg full with water and a person. Most apartment-building floor slabs handle that fine, but for upper floors of older buildings or light framed structures, check the load capacity with an engineer beforehand — that's a structural question, not a tub-selection one.
How does engineered stone for a tub differ from acrylic?
Cast marble and quartz composite are solid poured material built from mineral filler and resin, not a thin acrylic sheet over a frame. A stone tub is heavier (150–250 kg), holds its shape without losing rigidity for decades, and won't warp from boiling water — but it costs 2–4x more than an acrylic tub of the same size and needs a solid floor base.
Can I order a custom-shaped or custom-sized tub from China?
Yes — acrylic and stone tubs are molded to a custom geometry for a niche, bay window, or platform build-in, which is one of the main advantages of these materials over cast iron and steel, which only come in fixed factory molds.
Which tub suits a hotel or short-term rental (HORECA)?
For high-turnover guest properties, an acrylic tub with a reinforced backing is the usual choice — a good balance of price, weight, and repairability, since scratches can be sanded out on site. Premium rooms often go with a built-in stone tub for the visual effect of a solid, seamless basin.