Is an acrylic spa hot tub made of fiberglass?

When purchasing a hot tub, you'll often encounter descriptions of various materials, such as acrylic, fiberglass, resin, and synthetic composites.

Many people have a common question: Is an acrylic spa hot tub actually made of fiberglass? Or, what is the relationship between acrylic and fiberglass? Are they the same material?

To help you better understand the material structure of hot tubs, this article will delve into the relationship between acrylic and fiberglass from the perspectives of material properties, manufacturing processes, functions, and overall performance, and discuss why modern homes and spas tend to choose acrylic spa hot tubs.

Is an acrylic spa hot tub made entirely of acrylic?

Many consumers mistakenly believe that an acrylic spa hot tub is entirely made of "pure acrylic," but this is not actually the case.

Acrylic spa hot tubs are not entirely made of acrylic; they are a composite of two materials:

1. Surface layer: Sanitary grade acrylic sheet

2. Backing reinforcement layer: Fiberglass reinforcement layer

Therefore, an acrylic spa hot tub is not "made of fiberglass," but it does contain a fiberglass reinforcement layer for structural support.

In other words:

Acrylic spa hot tub = Acrylic surface layer + Fiberglass reinforcement layer (back reinforcement)

This is the most mainstream, stable, and durable manufacturing method in the modern hot tub industry.

Why does an acrylic spa hot tub need fiberglass? Can't it rely solely on acrylic?

This is the key question for understanding the relationship between the two.

1. Acrylic itself is relatively thin and requires a reinforcement layer for support

Acrylic sheets used in hot tub manufacturing are typically about 3–6 mm thick. Even high-quality sanitary grade acrylic cannot withstand the enormous pressure generated by water volume and the weight of a person.

2. Fiberglass possesses extremely high structural strength

Fiberglass has the following characteristics:

• High compressive strength

• High flexural strength

• Moisture and high temperature resistance

• Lightweight

• Structural stability

Therefore, it is ideal as a reinforcement material for the back of a bathtub.

3. Acrylic + Fiberglass = The most stable composite structure

This composite structure provides:

• Smooth, glossy, and antibacterial surface

• Strong, pressure-resistant, and stable inner layer

This is why mid-to-high-end brands on the market use this technology.

What are the fundamental structural differences between acrylic spa hot tubs and fiberglass bathtubs?

Although they may look similar on the surface, their structure and quality differ significantly.

Fiberglass Tub Characteristics:

• Primarily composed of fiberglass and resin

• Surface layer is a gel-coated material, not acrylic

• More prone to fading

• More easily scratched

• Surface may become rough over time

• Moderate durability

Acrylic Spa Hot Tub Characteristics:

• Surface layer is high-strength sanitary-grade acrylic

• Fiberglass reinforced back, but not the fiberglass surface layer

• High visual gloss

• Strong UV resistance

• Not easily faded

• Smooth surface, high hardness

• Longer lifespan

Therefore, although acrylic spa hot tubs also use fiberglass, their quality level is completely different from bathtubs made entirely of fiberglass.

In other words:

Fiberglass bathtub = Structural material + surface layer is also gel-coated resin

Acrylic spa hot tub = Fiberglass only for back support, surface layer is high-grade acrylic sheet

The two are completely different grades.

What role does fiberglass play in the manufacture of acrylic spa hot tubs?

Fiberglass primarily serves a reinforcing role, not for aesthetics or hygiene.

Here are its core functions:

1. Increased Structural Strength

Acrylic itself is flexible but not strong enough; the fiberglass reinforcement layer ensures the bathtub maintains a robust structure.

2. Prevention of Deformation

Hot tubs are prone to expansion under high temperature and water pressure, so fiberglass reinforcement ensures they maintain their shape.

3. Increased Load Capacity

A large hot tub filled with water can weigh hundreds of kilograms or even tons, making the fiberglass layer indispensable.

4. Extended Lifespan

The fiberglass structure enhances durability, allowing the acrylic spa hot tub to remain stable for many years.

Therefore, fiberglass is not used to replace acrylic, but rather to supplement its shortcomings, resulting in a superior overall structure for the hot tub.

Why isn't fiberglass used on the surface of an acrylic spa hot tub?

1. Fiberglass Surface is Not Smooth Enough

Fiberglass requires a gel coat, but this coating is prone to oxidation, fading, and wear.

2. Hygienic Acrylic: More Stain-Resistant and Easier to Clean

Acrylic is a non-porous material with the following properties:

• Does not absorb stains

• Does not easily breed bacteria

• Smooth to the touch

• Resistant to chemical corrosion

It is a more suitable surface material for human contact.

3. Acrylic Offers Enhanced Visual Appeal

• High gloss

• Saturated colors

• UV resistant

• Less prone to aging

Therefore, the surface layer must be made of acrylic, not fiberglass.

Does the manufacturing process of an acrylic spa hot tub rely on fiberglass?

Yes, most professional brands use the following process:

Step 1: Heating and Shaping Acrylic Sheets

The sheet is heated to a soft state using vacuum forming technology and shaped into a bathtub.

Step 2: Spraying a Fiberglass Resin Layer onto the Back

Fiberglass reinforcement material is sprayed onto the back of the acrylic sheet to make the structure thicker.

Step 3: Curing and Reinforcement

The fiberglass cures to form a strong supporting layer.

Step 4: Install the bottom support frame

This allows the bathtub to support greater weight.

Step 5: Sanding and cleaning, ready for final assembly

Therefore:

Fiberglass is an essential structural layer, but it is not the main material of the bathtub.

Why is an acrylic spa hot tub considered more premium than a fiberglass bathtub?

Mainly due to the following factors:

1. Surface material determines quality

Acrylic has a much higher gloss than fiberglass gel-coat.

2. Better UV resistance

Especially important for outdoor installations, as fiberglass is prone to fading.

3. Better stain resistance

Acrylic surfaces are smoother and do not attract stains.

4. Longer lifespan

The acrylic + fiberglass composite structure is stronger than pure fiberglass.

5. Higher scratch resistance

Acrylic has higher hardness and is less prone to scratches.

Therefore, although both use fiberglass, the acrylic spa hot tub is clearly of a higher grade.

Is an acrylic spa hot tub more suitable for spa use?

If you're choosing a bathtub for a spa, home spa, or outdoor spa, acrylic is a better choice because:

• More comfortable surface feel

• More upscale appearance

• Longer lifespan

• UV resistant and colorfast

• Good heat retention

• Less prone to cracking

This is why almost all mid-to-high-end hot tub brands use acrylic as the surface material.

Is an acrylic spa hot tub made of fiberglass?

The final conclusion is:

❌ An acrylic spa hot tub is not made of fiberglass.

✔ Its surface layer is acrylic, while the back reinforcement layer is fiberglass.

They are two different materials, each serving different functions:

• Acrylic: Beautiful, smooth, stain-resistant, UV resistant

• Fiberglass: Reinforces the structure, increasing load-bearing capacity and durability

The combination of both makes acrylic spa hot tubs one of the most popular, stable, and high-performance hot tub materials on the market today.