High Density Foam for Hot Tubs

R-Values and Density

• The R-value indicates the resistance of the insulation material to heat flow or loss, and the higher the R-value, the better the insulation. Foam insulation with a higher density does not necessarily mean a higher R-value, so when you choose insulation for your hot tub you should focus on the insulation value you need instead of the density.

Closed-Cell Spray Foam

• Closed-cell foam, made from polyurethane, has unbroken cells filled with gas containing hydrochlorofluorocarbons or HCFCs. The gas has high thermal resistance characteristics, which gives the foam an R-value of approximately R-7 to R-8 per inch. This insulation material sells in a spray-foam form and has a density of approximately 2 to 3 pounds per cubic foot. This type of insulation has a much higher density than open-cell spray foam, which typically has a density of less than 1 pound per cubic foot.

Expanding Foam

• Expanding urethane foam sells in liquid form, which becomes rigid as it sets. The density of expanding foam varies between two and 16 pounds per cubic foot of foam once expanded. The foam is sprayed into the cavity between the inner and outer walls of the hot tub and fills all the corners and angles. A density of four pounds per cubic foot is likely to be adequate for insulating a hot tub. The higher density foams set to an extremely rigid consistency.

Pour-in-Place Foam

• This slow-rising polyurethane foam takes a longer period to cure than other foam insulation products. The foam is poured into the insulation cavity and flows freely and naturally to fill the area, preventing air bubbles from forming. Pouring in additional substance to make it as full as possible as the foam settles helps it to compact and achieve the highest possible density. A density of 2 pounds per cubic foot results in an insulation value of R-5.9.

Foam Board

• Panels of rigid extruded or expanded polyurethane foam board have a very stable R-value and a long life span. The density is not as high as other types of foam insulation, and installation in a hot tub cavity may prove difficult unless the sides can be opened up. This type of insulation is inexpensive and does not require handling with safety equipment, so it is an option for homeowners on a low budget. Insulation panels with reflective foil facings mounted on them have R-values of R-7.1 to R-8.7 per inch.

Installation Requirement

• All foam insulation products used in residential applications need to be covered by a protective thermal barrier or to pass fire tests. The barrier must comply with the International Code Council evaluation service’s requirement to prevent the foam temperature from rising above 250 degrees F. during a 15-minute period. You can use foam insulation without a thermal barrier if it passes one of several ICC-approved compliance tests.