- Spa and hot tub shell materials are typically acrylic or thermoplastic. The shell has reinforced fiberglass or high-density polyurethane foam to strengthen the shell and allow for the connection of jets and plumbing.
- Manufacturers will typically heat the shell material and then place it over a mold. The mold will vary based on the style of the tub and number of seats or jets. A vacuum connected to the mold will suck the heated material into the mold, forming the shell, which hardens as it cools.
- Adding jets and other features to the spa or hot tub shell requires the manufacturer to cut into the shell. This does not weaken the shell since the reinforcing materials on the back of the shell help to connect the plumbing to the shell, which is typically thin material.
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