R-Value = Insulation efficiency

The R-value for hot tub covers is a numerical calculation that tells the insulation factor of hot tub covers. The higher the number, the better hot tub covers will keep the heat in and the cold out, and keep your heating bill down.

The R-value of a hot tub cover is determined by two factors, the thickness of the cover and the density of the foam core.

Foam Core Thickness

Hot tub covers come in varying thicknesses. Most hot tub covers are thicker in the middle and thinner at the edges so that rainwater will run off of the cover. This is called the cover’s “slope”. Typical cover slopes are 4” – 2”, 5” – 3” and 6” – 4”.

The R-Value is calculated by multiplying the R-factor of the foam density times the thickness of the foam. For example, if the cover’s slope is 5” – 3” or 4” thick on average, the R-Value would be the R-Factor times 4. The thickness of the hot tub cover is a larger factor in the overall R-Value than the density as will be explained below.

Foam Core Density

Hot tub covers come in varying densities of foam cores. Typical densities are 1.0 pound, 1.5 pound and 2.0 pound. The “pound” means the number of pounds of raw material is used per unit when the foam is made. The foam will be exactly the same thickness for each density, but the foam will contain more material, will be denser and therefore stronger.

R-Value Calculations - 5"-3" with 2.0#  vs. 6"-4" with 1.0#

Thickness is the critical factor for overall R-Value of hot tub covers. Keep in mind that the cover as a whole is a different R-Value calculation. The hot tub covers core is only one of the elements of the overall cover R-Value. The examples below are ONLY for the hot tub covers foam core, and will show that the cover’s thickness is a more important factor than the cover’s foam density.

Lets compare upgrading a 5"- 3" slope hot tub cover to 2.0# foam with a 6" - 4" slope with 1.0# foam.

5” – 3” slope hot tub covers with 1.0 pound foam

Average foam thickness = 4”

1.0 pound foam’s R-factor is 4.17 at 40 degrees F

R-value of the foam only would be 4” X 4.17 = 16.68

6” – 4” slope hot tub covers with 1.0 pound foam

Average foam thickness = 5”

1.0 pound foam’s R-factor is 4.17 at 40 degrees F

R-value of the foam only would be 5” X 4.17 = 20.85

Now, if the same 5” – 3” slope cover is upgraded to 2.0 pound foam:

5” – 3” slope hot tub covers with 2.0 pound foam

Average foam thickness = 4”

2.0 pound foam’s R-factor is 4.76 at 40 degrees F

R-value of the foam only would be 4” X 4.76 = 19.04

The the 6” – 4” with 1.0# foam has a higher R-Value than 5” – 3” with 2.0# foam !