Your bathtub is likely made of acrylic, fiberglass, cast iron, or steel. Because bathtubs look very similar from a distance, you can identify your specific material at home using three quick, simple tests.
The Magnet Test
How to perform it: Place a strong magnet against the bathtub wall. If the magnet sticks firmly, your tub is made of cast iron or steel with a porcelain enamel coating. If the magnet doesn't stick at all, you have a fiberglass, acrylic, or stone-based material.
To quickly tell if your tub is fiberglass or acrylic, press on the wall and inspect the finish. Fiberglass is lighter, more flexible, and prone to fading, while acrylic is thicker, rigid, and non-porous. You can rule out metal entirely if a magnet doesn't stick.
To quickly tell if your bathtub is steel or cast iron, first use a magnet. Both are magnetic, but cast iron is significantly heavier (weighing 300-500 lbs), doesn't flex when pushed, and makes a dull, solid, bell-like sound when tapped. Steel tubs are lightweight, have a higher-pitched, tinny sound, and feel thinner at the edges.
To quickly tell if your tub is porcelain or acrylic, use the magnet and tap tests:
Regarding cleaning with your standard household products, some will work better for cleaning acrylic tubs than others. An excellent example of one that works well is Dawn dish soap. Dawn is gentle enough to use on acrylic surfaces and could help cut through the dirt and grime.
If it's steel or porcelain the magnets work. If it's acrylic they just float around. Historically, all tubs were cast iron. Plastic/fiberglass tubs are a relatively new invention.
Bathtubs in the 1950s were primarily made of cast iron coated in porcelain enamel. Stamped steel also began to emerge as a lighter, cheaper alternative. Unlike earlier clawfoot models, 1950s tubs were built-in, recessed styles known as "apron" or "alcove" tubs.
Yes, a magnet will stick to cast iron. Because cast iron is approximately 93-96% iron, it is a highly ferromagnetic material.
Identifying unmarked cast iron requires examining specific details like handle shapes, pour spouts, heat rings, and size markings. Major American foundries—such as Lodge, Wagner, and Birmingham Stove and Range (BSR)—produced "unmarked" lines without brand logos, often sold in hardware stores, to bypass brand-name premiums.
As a result, acrylic bathtubs remain highly relevant, especially in freestanding and soaking designs, but are now being incorporated more intentionally rather than automatically included in every bathroom.
Dish soap isn't just for dishes; it can serve as an effective cleaner for your bathtub when you're alone at home. The surfactants in dish soap break down grease and grime, making it an efficient choice for tackling soap scum and dirt in your bathroom.
A fiberglass tub looks like a clean, shiny, one-piece unit, usually white or off-white, with a slightly less glossy finish than acrylic. It often comes as a standard three-wall alcove (tub-and-shower) combo and feels lightweight and slightly flexible if you press on the sides.
To tell if a bathtub is fiberglass or acrylic, press firmly on the side: fiberglass flexes, feels softer, and is often duller, while acrylic is more rigid, glossy, and warm to the touch. Fiberglass often fades or scratches, particularly at the bottom, and can sound hollow when tapped.
An acrylic tub typically lasts between 10 and 15 years, but with proper care and professional installation, it can last 20 years or more. The lifespan largely depends on the quality of the material, how often the tub is used, and how well it is maintained over time.
What Tubs Do Plumbers Recommend?
To tell if your bathtub is cast iron or steel, grab a strong magnet. Both metals are magnetic, but you can identify cast iron by its thick, heavy build (often weighing 300+ lbs), a solid "thud" sound when tapped, and its thick edges. Steel tubs are much lighter and make a hollow, higher-pitched "tinny" sound.
The Bible does not mention magnets. The concept of magnetism and magnetic forces was not scientifically understood by the ancient cultures that wrote the biblical texts.
Gray Cast Iron: Produces short, red-orange sparks with a lot of bursts, both at the base and along the spark trail. Carbon Steel or Cast Steel: Produces long, yellow sparks with fewer bursts, usually only at the tip.
Old bathtubs are most famously made of cast iron coated in a durable, glassy porcelain enamel finish. While cast iron is the most iconic vintage material, older tubs from different eras were also constructed from a variety of other materials.
The four primary types of bathing include showers, tub baths, partial baths, and bed baths. These methods are categorized by mobility requirements, ranging from active washing to assisted care.
Your bathtub is magnetic because it is made of steel or cast iron. While the tub might look like pure white porcelain, it actually has a thick metal core coated in a porcelain-enamel glaze. This metal core is what allows magnets to stick to the side of the tub.
To quickly tell if your bathtub is porcelain, use a strong magnet and listen to the sound it makes. A magnet will stick firmly to a porcelain-enameled metal tub. If tapped with a coin, porcelain produces a high-pitched, bell-like ring and feels completely rigid with no give when pressed.
First off, if your "pure gold" is magnetic, then there is iron inside (or maybe nickel). In fact, this is one way to tell if jewelry is actually gold. If it's not attracted to a magnet then there is no iron - but it still might not be gold. Scammers have been known to coat lead, copper, and aluminum.
Yes, you can use Bar Keepers Friend on a porcelain tub. Its mild abrasive and oxalic acid formula effortlessly cuts through soap scum, rust, and mineral stains. However, because it contains abrasives, it is important to scrub gently and use the right tools to avoid scratching or dulling the porcelain's shiny finish.