Hot Tub Covers and the R-Value -SpaCap

The Myth of R-Value and traditional foam filled Hot Tub Covers.

R-value is a form of measurement of the ability to resist heat transfer for materials like the fiberglass insulation in your house or maybe the insulating foam in hot tub covers. The intent is that, the greater the R-value, the better the heat storage and, heat retention would be the primary job of any hot tub cover.

Most industries using R-values are regulated by FTC standards. Commercially sold insulation must pass independent tests created by American Standards and Testing Methods (ASTM) so as to be advertised or marked using their R-Value.

The Misled Masses: As there is no FTC recognized independent test for spa covers, So ANY stated R-value stated by a spa cover dealer is in reality an unregulated, unmonitored “interpretation” of a given insulation value. It is open to misrepresentation and abuse, from adding the R-value of an air space between the water and the bottom of the cover, spacing between the vinyl and the cover insulation, or simply blatantly inflating the fictitious number. Some hot tub dealers state exclusively the known R-value of the insulation itself, but of course that doesn’t mean that it was tested and endorsed to use in hot tub cover applications.

The R-value of the actual foam insulation, no matter the density, is ONLY rated for use in DRY building applications! Which signifies the fact that the R rating of the foam is only applicable should it happen to be applied in a wall, attic or floor. Because should it were to be used in a moist environment, that type of insulation would fail quickly.


Foam Density and Foam Thickness.

These two factors that spa cover dealers claim affect the R-value of a spa cover, when in fact that R rating itself has nothing to do with the foam when it is used in a hot tub cover. Actually, it is as misleading as the idea that a taper on the cover will really keep it from getting heavy.

True, the foam density and thickness would have a bearing on the insulation properties In the event the Usage of the foam were in compliance with the designed use of a completely DRY environment.

Regardless if the dealer claims his spa covers are made with the most costly spa cover foam (rigid cellular polystyrene thermal insulation) available, resists breakage, vapor absorption and chemical damage more than all the others they’ve tested. The truth is, R factor is NOT something they test, and RESISTING breakage and saturation are not the same as AVOIDING it altogether.

When looking for and comparing spa covers, ALL claims associated with R-value of a cover that has foam are totally unsubstantiated. Foam Density and Foam Thickness do not have any ADDED R VALUE, since the foam is not designed to be applied over a wet environment. Most spa cover dealers repeat exactly the same numbers and consequently hot tub owners have been trained to believe the lie. Some dealers employ some fancy charts to substantiate their claims, however the main point is those claims cannot be in accordance to the ASTM.

Myth Busted!

R-value testing of materials is completed at room temperature, and doesn’t take into account moisture and vapor. In the spa environment, there is hot water and good amounts of steamy moisture. Each of which will dramatically reduce the R-value of any foam. A spa at 105 degrees will defeat the R-value of any foam tested to use in a dry application.

Don’t allow the R-value of foam be considered the measurement for spa cover quality. Instead search for a spa cover with NO FOAM. A hot tub covers that use air filled chambers as an alternative for rigid foam boards will out preform any other, in any test or real hot tub application. (Hello, SpaCap)


Don’t be fooled by claims of high density and weight, vacuum wrapped in sheets of heat welded polyethylene, sealed in heavy gauge marine grade vinyl, with chemical resistant scrim and stitching. It won’t insulate as well. It will definitely still become saturated, warped or broken. It truly was obsolete thirty years ago.