InsaneJournal

The exterior of hot tubs is also referred to as the “spa shell”. It is made of the surface as well as the understructure, which are attached together during the process of manufacturing the item. The surface is the very factor that gives the look, the color and the feel of the entire spa, as well as the hot tub covers found on them. This should be able to resist the deterioration with the repetitive use of chemicals and of course the inevitable wear and tear. Some spa shells that come in high-quality are coated with a special product that conveniently protects the surface from bacteria.

There are two methods in manufacturing a spa shell:
a.vacuum form an acrylic base by placing a sheet over the mold, melted by the heat of a heater, while tugging the vacuum unto the mold
b.rotational molding, which uses polyethylene powder inside a mold made of aluminum, which is spun and heated at the same time

The understructure of the spa shell is the material that provides the strength that is needed to support both the hundred gallons of water as well as the people who will be sitting within the tub for multiple hours. For the substructure of the tub, companies would use fiberglass, which is very durable, but then others still utilize various types of plastics. Some manufacturers also make use a self-support shell, while others would utilize wood or metal to be positioned under the seats or in areas vulnerable to stress for secondary support. For the rim, manufacturers would use perimeter frames of metal or wood for support.