Fiberglass vs. Cast Iron Bathtub: The Big Difference


Fiberglass vs Cast Iron Bathtub

Renovating a bathroom can be a lot of fun, but it involves making plenty of important decisions, such as the type of bathtub you’re going to install. Fiberglass and cast iron are two of the most popular materials, but they are practically opposites when it comes to the pros and cons of each.

Fiberglass tubs are lightweight, inexpensive, and easy to install. Cast iron tubs offer timeless beauty, excellent quality, and a long lifespan. The best option depends on your bathroom’s design and personal preferences. 

Read on to discover more about fiberglass and cast iron bathtubs so that you can make an informed decision. 

 

Fiberglass vs. Cast Iron: A Comparison

Best Ceramic Tiles for Rental Bathroom
Alcove fiberglass tub

Choosing a bathtub can feel overwhelming. They come in various shapes, sizes, and materials. Which factors should you consider if your preliminary choices are fiberglass and cast iron?

When deciding between both materials, considering the following features may help you decide: 

  • Cost 
  • Ease of installation
  • Weight
  • Flexibility
  • Heat retention
  • Durability
  • Longevity
  • Maintenance 

Fiberglass tubs consist of molded plastic reinforced with glass fibers, making them lightweight, flexible, and durable. On the other hand, cast iron bathtubs contain iron alloys, carbon, fused porcelain, and an enamel layer, resulting in a heavy, chip-resistant, and long-lasting bathroom accessory.

Below is a helpful table explaining the key points to consider when choosing between fiberglass and cast iron bathtubs.

 FiberglassCast Iron
CostAffordable Expensive
Ease of InstallationVery easy to installChallenging to install
WeightLightweight (average weight is 70 pounds/31.75kg)Extremely heavy (average weight is 350 to 500 pounds/158 to 226kg)
FlexibilityWide range of shapes and sizes Limited styles (mostly traditional and vintage)
Heat RetentionPoor heat retentionExcellent heat retention
Durability Brittle and prone to scratching and chipping
Durable, scratch and chip-resistant
LongevityHas a typical lifespan of 15 years, after which the color will fadeCan easily last for over seven decades, and you can refinish it if your tub is no longer in fashion
MaintenanceChallenging to clean

Easy and inexpensive to repair cracks and scratches yourself

Tub must be thoroughly dry after use as fiberglass is porous
Easy to clean

Cracks and chips are rare, but these are challenging and expensive to repair

Prone to rusting if cracks form

I’ll discuss these points in more detail below.

 

Which Tub Type Is Cheaper?

Acrylic vs Cast Iron Tub
Cast iron claw foot tub

Fiberglass bathtubs are cheaper and an excellent choice if you’re on a strict budget. In contrast, cast iron tubs are much more costly, sometimes triple the price of fiberglass bathtubs.

For example, the Signature Hardware Cast Iron Clawfoot Tub from Amazon.com has a classic and elegant style and has been designed to last a lifetime. It has a capacity of 34 gallons. However, it is over three times more expensive than a fiberglass bathtub with a 48-gallon capacity, namely the American Standard Studio Integral Apron Bathtub.  

Consider this: Over a 50-year period, you would probably replace your fiberglass tub three times, costing around the same as installing a cast iron bathtub. 

Fiberglass bathtubs are fantastic if you’re on a budget, have a small bathroom, and want an ultra-modern tub. 

 

Fiberglass vs. Cast Iron Bathtub: What’s Easier To Install?

acrylic vs fiberglass bathtub installation

Fiberglass bathtubs are easier to install because they are lightweight, and they can be a DIY project. Cast iron bathtubs require professional installation.

If you have intermediate-level plumbing skills and are tempted to install a fiberglass bathtub yourself, it may be possible. Be sure to read my post about How Hard Is It to Install a Bathtub?  

In contrast, cast iron bathtub installation is more complex, challenging, and expensive, and you’ll likely need to call in a professional for assistance. 

 

Fiberglass Tub: Ideal for Second Floor

Since fiberglass is lightweight, your bathroom floor should have no problem supporting the weight of the full bathtub with a bather in it. This makes a fiberglass bathtub ideal if your bathroom is on the second floor. 

Better yet, if you are replacing your current bathtub with a fiberglass one of the same size, you can usually just drop it in, connect it to your bathroom’s plumbing and seal the edges. 

That said, it’s important to install your fiberglass tub securely. The lightweight and flexible construction means a fiberglass tub can shift easily, especially if it’s used a lot. 

 

Cast Iron Tub: Might Need Extra Floor Supports

Installing a cast iron tub is much more complex. To start, you need to make sure that the underlying floor will support the tub and that the weight of the tub won’t damage the floor. 

As a layperson, you won’t be able to make this assessment on your own, so you’ll need to consult with a structural engineer or construction expert, and this comes at a cost. 

If the structural engineer finds an issue with the floor’s structure, they may need to reinforce the joists or treat the flooring before installing the tub. 

A cast iron bathtub’s heavy weight also means that it’s too heavy for one person to lift, and you won’t be able to install it on your own. If you’re considering cast iron, be sure to check out my post on The Hidden Costs of a Clawfoot Tub.

 

Which Bathtub Is Heavier?

Acrylic vs Cast Iron Tub
Cast iron claw foot

Cast iron tubs are heavier. Fiberglass bathtubs have an average weight of 70 pounds (31.75kg), while cast iron tubs can weigh between 350 and 500 pounds (158 to 226kg). 

Cast iron’s heavy weight gives it a high-quality and luxurious feel and finish. It also provides exceptional stability to easily stand on its own or be suspended on claw feet. 

Some people want an extra wide cast iron soaking tub, even one that can accommodate two bathers. This is quite a hard tub to find, and of course, the larger size will add to the overall weight. 

Fiberglass tubs usually have a gel coating, making them feel plasticky. If you want a freestanding bathtub, a fiberglass bathtub won’t do the trick—these tubs need to be well-supported with a frame. 

If you do have your heart set on a freestanding tub and aren’t sure about cast iron, read my guide to picking the right freestanding bathtub to get all your options.

 

Which Has More Flexibility?

Cast Iron vs Fiberglass Tub
Drop-in fiberglass bathtub

 

Fiberglass tubs offer more flexibility. They come in a broad range of shapes and sizes, so you’ll be spoiled for choice. If you’re looking for a uniquely-designed bathtub in an interesting shape, fiberglass is an excellent choice. 

Cast iron bathtubs, on the other hand, are usually larger than fiberglass ones and come in a limited range of shapes. Their larger sizes can make them unsuitable for small bathrooms, and the classic, vintage style may not suit houses with an ultra-modern design. 

 

Cast Iron or Fiberglass Tubs: Which Offers Better Heat Retention?

Sunburn - try a milk bath
Drop-in fiberglass bathtub

 

Cast iron tubs offer better heat retention. They absorb and lose heat more slowly than fiberglass. Fiberglass heats up quickly but loses heat rapidly, offering poor heat retention.

When filling a fiberglass tub with hot water, you’ll notice that the fiberglass heats up quickly. Unfortunately, it soon loses the gained heat, and you’ll need to add more hot water if you want to enjoy a long hot soak.

Cast iron tubs take about ten minutes to heat up after being filled with hot water. However, cast iron retains heat exceptionally well, and you’ll notice that your bathtub will feel warm even after the bathwater has cooled. 

 

Fiberglass vs. Cast Iron Bathtub: Which One Is More Durable?

extra-wide cast iron soaking tub
Extra wide cast iron bathtub

 

Cast iron tubs are more durable than fiberglass tubs. They contain iron alloy, porcelain, and a heavyweight enamel coat, making them highly scratch and chip resistant. 

It is almost impossible to chip or crack a cast iron tub, but it can happen if you exert enough force. 

Fiberglass contains tiny glass fibers in molded plastic, making it vulnerable to scratching and chipping. If you accidentally drop a heavy object into your fiberglass tub, it may shatter and form large cracks. 

 

Which One Lasts Longer?

Fiberglass vs Cast Iron Bathtub
Alcove fiberglass bathtub

 

Cast iron tubs last longer, typically seven decades or more. Fiberglass bathtubs have a typical lifespan of 10-15 years, after which they’ll show visible signs of wear and tear, scratching, and fading. 

Color-fading is the most noticeable sign of an aging fiberglass bathtub. Over time, the tub’s shiny gel coating wears off, and the tiny glass fibers become cloudy, making the tub look dull. The bathtub may become an eyesore in your bathroom, prompting you to replace it. 

Unfortunately, this tub material is not a candidate for a bathtub liner. Getting a professional to refinish your fiberglass tub will cost around $500 and so you might as well just replace it. 

However, for about $170, you can try a DIY refinishing product. (I recommend the nontoxic Ekopel 2K Bathtub Refinishing Kit available on Amazon.com.)

Cast iron bathtubs can easily last as long as you do—seven decades or more! And if you find the color unfashionable or you want to remodel your bathroom, you can easily recoat it in your desired shade.

 

Fiberglass Tubs vs. Cast Iron Tubs: Which Is Easier To Maintain?

Height of Bathroom Sconces

 

It’s easier to maintain a cast iron bathtub because you don’t have to dry it after each use. You can get away with only cleaning it weekly, and you’ll rarely need to treat scratches or chips.

Fiberglass tubs are challenging to clean because they scratch easily, and you need to use a gentle cleaning method. If you’re not careful, your tub can get permanently stained. Fiberglass is porous and readily absorbs dirt, shampoo, and other substances. 

If you don’t dry your fiberglass tub thoroughly each time after using it, it will absorb the minerals in the water, and if there is enough mineral accumulation, the tub will look dull and patchy. 

 

Clean a Fiberglass Tub Twice Per Week

 

The best way to prevent staining and mineral deposits in your fiberglass tub that is used daily is to clean it twice a week. You can do this with a gentle, non-toxic bathroom cleaner. Watch the video above for details.

Not cleaning or drying your fiberglass tub at least twice a week can also promote bathroom mold, and these black stains can be impossible to get out of fiberglass. 

Accidental scratches or minor cracks in your fiberglass tub are easy to repair, and you can do it yourself by buying an inexpensive repair kit online. 

 

Clean a Cast Iron Tub Once Per Week

Cast iron bathtubs are easy to clean, but you should avoid using highly abrasive or acidic cleaning methods as these could damage the enamel coating. If you have a cast iron tub, you can get away with only cleaning it once a week due to its rigid composition.

Chips or cracks in cast iron tubs are rare, but if these occur, you need to attend to them as soon as possible because they can lead to rusting. Unfortunately, it’s not straightforward to repair cracks or chips in cast iron tubs. You’ll need to call in a professional, which can be costly. 

 

Should You Get a Fiberglass or Cast Iron Tub?

Cast Iron Tub vs Fiberglass Tub
Cast iron clawfoot bathtub

 

Now that you know the differences between fiberglass and cast iron bathtubs, which one is better for you? 

You should get a fiberglass tub if you’re on a budget or want to be able to easily remodel your bathroom in the future. You should get a cast iron tub if you want a durable bathtub that doesn’t need much maintenance and you enjoy taking long, luxurious bubble baths.

Cast iron tubs are more expensive than fiberglass tubs, but installing one could save you money in the long term. 

However, you might opt for a cast iron tub if you like the feel of a high-quality tub, want a claw foot model, and enjoy lingering in a relaxing bubble bath. 

Note: If you’re embarking on a bathroom remodel, be sure to sign up for my newsletter. You’ll get my Save Big $$$ Cheat Sheet full of designer hacks that can literally help you save thousands of dollars. Just fill out the form below.

Shana

Shana Burg is a bath enthusiast, content strategist, and award-winning writer. She is the founder of bathtubber.com.

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