Confessions of a ThermoSpas Employee

The shell surface may not be the first thing you consider when you decide to buy a hot tub…you’re probably more concerned with how great that warm water’s going to feel when you get in!  But the shell surface is a very important component of your hot tub.  Other elements, such as pumps or heaters, are fairly easy to repair or replace if something goes wrong. However, if the hot tub shell malfunctions, it is more than likely that the entire spa will have to be replaced.

There are two major types of material used in manufacturing hot tub shell surfaces: OAS and acrylic. Both have good impact resistance and will take a fair amount of abuse. However, there are some significant differences between the two:

OAS (Olefin Acrylonitrile-Styrene)
Many manufacturers utilize OAS as the shell surface material under different names (such as Rovel, Endurol, or Ultralife), however, they are all essentially the same materials. Compared to acrylic OAS is a less expensive material and may produce a slight saving on the total cost of your spa. In addition, some people have found that they prefer the simplistic appearance of this plastic material to the luster that is typical of acrylic.

A negative to OAS is that it is a porous material, which can make the surface more difficult to clean than acrylic. In addition, OAS is usually available only in light solid colors, primarily white, which only adds to the difficulty in its cleaning. Darker colors are avoided with OAS because it was found that when those spas were drained, there would be significant color variations between the areas above and below the water line. Stain resistance can also present a problem for OAS. Stains that are common with spas can include shoe polish, lipstick, tar, grease, and marker. These, and many other stains, are difficult to remove from OAS, especially for the lighter colors that cannot hide the stains. An additional problem for OAS is the staining that occurs from the use of well water or water with a high iron content. It can be nearly impossible to remove rust stains from OAS, and it is not recommended to use OAS if you have well water or water with a high iron content.

OAS can also limit the types of chemical sanitizers that you use. Most OAS manufacturers restrict you from using chlorine to sanitize the spa water because the chlorine can discolor the plastic surface.

Acrylic
From two and three color marble patterns to simulated granite, acrylic offers a wide variety of colors and styles from which to choose. A major advantage of acrylic is its smooth, high-gloss finish that gives the hot tub shell surface a luxurious sheen and is easy to clean, unlike the textured surface of OAS. Its hard, non-porous surface prevents dirt from accumulating and resists stains, allowing you to maintain your hot tub simply and easily. Lastly, acrylic’s durability allows any type of chemical sanitizer to be used. Due to all of the inherent benefits that acrylic provides, most manufacturers have chosen to use acrylic as their shell surface material.

It is highly recommended that you look for a continuous cast acrylic, which offers better durability than the co-extruded types. Tests have shown that co-extruded acrylic does not have the wearability that continuous cast acrylic does. Co-extruded acrylic tends to lose its luster over a period of time. Continuous cast acrylic contains UV inhibitors that are inherent in the product, protecting the shell surface from the harsh rays of the sun and from the damaging abuse of chemical sanitizers for decades. Finally, continuous cast acrylic is more resistant to chemical abuse and crazing than OAS, ensuring both a beautiful and durable spa. By utilizing a high quality acrylic, your hot tub can look virtually new five to ten years after purchase.

A recent innovation that has separated one continuous cast acrylic supplier from the rest is the introduction of Microban®, antimicrobial product protection. Microban® is not a coating, but an additive that is impregnated into the acrylic, and inhibits the growth of bacteria that causes odor and stains. While the entire hot tub shell is protected, a major advantage is that it protects the area above the waterline. Areas above the waterline do not benefit from the use of chemical sanitizers, and are usually defenseless to bacteria. Microban® helps to preserve the appearance of the shell’s surface, as well as making the shell easier to clean. Microban® antimicrobial product protection is designed to last for the life of the hot tub.

Whew…that’s a lot of information.  But it’s important because ensuring you have a reliable shell surface is essentially ensuring that you have a reliable and well built hot tub!