What Do I Insulate a Hot Tub Shell With?

Hot Tub Operations

A hot tub pool makes for a relaxing getaway as well as a therapeutic aid for achy muscles and joints. The type of insulation materials used in the making of a hot tub shell has a significant bearing on how long it will take to heat up the water. A well-insulated shell also helps the water to retain the heat for longer periods of time. Other factors, such as an indoor versus an outdoor tub and the average indoor or outdoor temperatures, also affect a hot tub’s energy efficiency rates. In effect, the longer a tub can keep the water warm, the lower the costs to run it.

More than 70 percent of the hot tubs sold in the United States use foam materials for insulation purposes, according to Spasearch, a spa and hot tub resource site. Foam insulation materials may consist of open-cell packaging-type foam or a closed cell polyurethane material. The two types differ in terms of water-absorption effects and density, or thickness. Polyurethane foam has a multi-layer, high-density consistency that doesn’t absorb water. The open-cell packaging-type has a low density, which limits its ability to insulate a hot tub shell. One way to tell whether a hot tub uses one or the other is to knock on the side of the shell. A solid sound indicates the presence of high-density insulation material.

Hot tubs made with multi-layered insulation — also known as blanket insulation — use layers of insulation between the hot tub cabinet and shell walls. The effectiveness of a multi-layered design depends on the R-value of the insulation material. The R-value indicates how well a material prevents heat from traveling through it, so a high R-value provides the best effect in terms of keeping tub waters warm. A well-made hot tub design will have insulation materials under the base of the tub as well as along tub walls. This type of setup also allows for easy access to hot tub components for repair purposes.

A single layer of insulation offers little cost savings for hot tub owners. Single-layer designs consist of a layer of polyurethane insulation along the base of the hot tub shell. While such a design provides minimal insulation, it does offer some cost savings, especially if the hot tub is situated indoors. Unlike multi-layered or foam insulated shells, single-layer designs offer little in terms of sound-proofing effects. Thick insulating materials can make for a quiet-running hot tub.