The spa shell is one of the most important components to consider when you're thinking about purchasing a hot tub. Most of the components like pumps or packs are relatively easy to repair or replace if needed. However, if the spa shell has manufacturing defects or cracks later on down the road, it will be difficult to find someone willing and able to repair it. If you do find someone who can and will repair it, the repair will be costly, and if the damage is too extensive to repair, you could end up having to replace the entire shell (also costly).

Most spa shells are made up of a minimum of two components that are melded together: the shell's top surface (what you see) and a substructure behind the shell (that you don't see). The shell's top surface is its color and texture and any special features that protect it from wear and tear. The substructure provides the shell's structural integrity and strength.

There are several different spa shell materials that are used in the industry. A short description of each material follows.

Vinyl:
Vinyl is typically used in inexpensive soft-sided hot tubs. Spa shells made out of vinyl are especially vulnerable to both chemical and wear and tear damage. Hot tubs manufactured with a vinyl spa shell are typically the lowest-priced hot tubs you can buy. However, it is important to remember that "you get what you pay for."

Acrylic backed by Fiberglass:
Acrylic is the most widely-used spa shell material and it offers the widest range of color and texture selection. Generally, acrylic spa shells are have a fiberglass compound substructure. The fiberglass substructure is attached (much like gluing) to the acrylic using bonding resins. The quality of this adhering process by the manufacturer depends on several things:

The Thickness of the Acrylic:
Thicker is obviously better, but it can be difficult to determine how thick a particular spa shell is. In the manufacturing process a flat acrylic sheet is heated and vacuum-formed (sucked down into) onto a mold. If done improperly, the spa shell can have "thin" areas, especially in curvy areas and on the walls.

The Substructure:
The highest quality substructure occurs if each layer of the fiberglass is hand-rolled. This prevents air bubbles, which can lead to delamination.

Acrylic backed by ABS plastic:
On the surface, this type of spa shell looks looks very similar to the acrylic that is backed by fiberglass. However, instead of adding a stiffening agent such as fiberglass, the this type of spa shell has the acrylic backed by (co-extruded with) a sheet of ABS plastic. ABS plastic is impact-resistant and when co-extruded properly, rarely separates from the acrylic surface. The downside of this type of spa shell is that it is weaker than a fiberglass- backed acrylic spa shell so the space between the shell and cabinet needs to be filled with full foam for additional support.

Most hot tubs that are foamed this way will have cabinets that cannot be removed. This can possibly complicate future repairs involving plumbing that is buried in the foam. Also if the hot tub cracks, it can be virtually impossible to repair.