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Spa Pool Shell Construction Guide | HotSpring Spas

Spa Pool Shell Construction Guide

Your spa pool's shell is tasked with holding the water inside your tub and is a key determining factor in how long the spa lasts. As a surface constantly exposed to water, chemicals and humans, it must be strong enough to withstand years of use as well as the occasional mishap. The best shells combine longevity, efficiency, beauty and functionality.

Spa pool shells come in a variety of materials, each possessing strengths and weaknesses. Learning more about what spa pool shells are made of can give you a better idea about which spa pool will be best suited to your needs.

Until the 1970s spa pool shells were primarily made of wood, but today only a few timber manufacturers remain. Most modern spa pool shells are made from vinyl, acrylic or rotomoulded plastic, while other materials like cement, stainless steel, fibreglass and inflatable PVC can also be used.


Vinyl spa pool shells

Some spa pools are constructed through a process in which a vinyl liner is placed over a frame made from another material, such as cement – the same method frequently used in swimming pool construction. As such vinyl liner spa pools are commonly found attached to inground pools.

While often inexpensive, particularly when part of a package deal with a swimming pool, these spas don't retain heat well. What you save on the sticker price may be eaten up by the cost of the electricity it takes to keep your spa pool warm. Vinyl isn’t particularly durable either; a vinyl spa pool shell is more likely to crack or tear than a shell made from other, stronger materials. Continuous exposure to chlorine will fade the colour of your vinyl spa pool liner, while an incorrect balance of chemicals in your spa pool can damage it.

Rotomoulded plastic spa pool shells

To create a rotomoulded spa pool you begin with plastic powder and a mould. The powder is inserted into the mould, heated until it melts, and then rotated until it covers the whole surface in a smooth and even layer.

Unlike the glossy surface of acrylic shells, rotomoulded plastic shells have a dull matte finish. Compared to acrylic shells, rotomoulded plastic shells are also relatively lightweight, due to the fact that the plastic is so efficiently and evenly distributed. This results in a lighter and more easily transportable spa pool, which may give you more options as to where it may be placed in your yard or on your deck.

The downside of rotomoulded spa pools is in their relatively inefficient heat retention. As with spa pools built with vinyl liners, the initial savings from their lower purchase price tend to be eroded over time, as owners of rotomoulded spa pools pay more in electricity than owners of more energy-efficient spas.

The upside of rotomoulded spas is that they can be produced at a lower cost and have a life as long as a premium spa.

Acrylic spa pool shells

An acrylic spa pool shell is made from a single sheet of acrylic. The sheet is heated until it begins to soften, then it’s placed over a mould. Vacuums suck away any air trapped between the mould and the acrylic, creating a smooth and perfectly formed shell. After the acrylic has cooled and hardened, it's reinforced with a combination of resin and fibreglass to further strengthen it.

Some acrylic shells are formed through a slightly different process: a layer of acrylonitrile butadiene styrene – also known as ABS – is applied to the sheet before moulding. The resulting spa pool shell is durable, beautiful and energy efficient. (Check out this video to see exactly how acrylic shells are formed.)

Owners of acrylic spa pools can expect them to withstand normal wear and tear for many years without showing signs of damage. Acrylic spa pools can be produced in a wealth of gorgeous colours and patterns, and when paired with high-quality insulation such as multi-density foam or FiberCor®, acrylic spa pools retain heat incredibly well if fully insulated. 

Acrylic spa pools are heavier than rotomoulded spa pools, making them more difficult to move, so they work best as a permanent installation in your backyard or on your deck. While glossy acrylic tubs are more expensive than vinyl or rotomoulded plastic versions, their excellent temperature retention translates to lower energy needs than other spa pools. Add in their durability, and these high-quality spas often end up cheaper in the long run!

While spa pool shells made of other materials have some advantages, acrylic shells are the choice of spa pool connoisseurs. If you value quality, performance and appearance, look no further.

Hot Spring®  spas only use ‘closed cell acrylic’ while other manufacturers use cheaper ‘open cell acrylic’. With closed cell acrylic, you do not get staining at the water line or contaminants in the spa water entering through the acrylic sheet. Under normal operating conditions, the colour will not bleach out of the acrylic sheet as it does on ‘open cell’ acrylic. The sheet is 2-3 times thicker than ‘open cell’ (which so much more expensive!). The thicker the sheet means that in the moulding process it can be drawn deeper and steeper. This helps give the spa pool wider seats and at a more comfortable angle for the back and larger foot well. 

This insightful design decision made over 40 years ago means Hot Spring®  spas have a greater internal volume, water up to your neck, comfortable seating and plenty of leg space. Just one of the many design decisions made by Hot Spring®  that make them the world's No.1 selling spa brand.

Choosing the right shell is just one of the decisions you’ll need to make in order to find your perfect spa pool, which is why our experts are ready to help you understand how to make the right choice. For a better idea of which spa pool shell would be best for you, visit your local spa pool dealer, who can answer all your questions and even offer a test soak!


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