What Is the R-Value of a Hot Tub Cover?
How R-Values Work in Spa Covers
The R-value is a measure of thermal resistance,[1] or ability of heat to transfer from hot to cold, through materials (such as insulation) and assemblies of materials (such as walls and floors). The higher the R-value, the more a material prevents heat transfer. R-value depends on materials’ resistance to heat conduction, as well as the thickness and (for loose or porous material) any heat losses due to convection and radiative heat transfer. However, it does not account for the radiative or convective properties of the material’s surface, which may be an important factor for some applications. R varies with temperature, but in construction, it is common to treat it as being constant for a given material (or assembly). It is closely related to the thermal transmittance (U-value) of a material or assembly, but is easier to manipulate in some calculations since it can be simply added for materials and assemblies that are arranged in layers, or scaled proportionately if the thickness of a material change.
Simply Stated: What the R-Value of a Spa Cover Means
To help the consumer compare the R-Values, certain standards have been put in place for industries to follow when referring to their products. The following information has been put together to help you the next time you are considering purchasing a spa cover.
1) In the case of spa covers the R-Value should reflect ONLY the foam itself Ideal™ Spa Covers then seals the foam inside the VPB3000 and uses the highest quality marine grade vinyl, which increases the R-Value; this should not be reflected in the advertised R-Value.
2) The R-Value will increase as the air temperature on the cold side of the insulation decreases. In other words, if you tested the insulation at 75 degrees Fahrenheit and then again at 25 degrees Fahrenheit, you will get a higher R-Value at 25 degrees Fahrenheit. ASTM has not specified a temperature that spa covers need to be tested. However, the air temperature must be disclosed when an R-Value is stated.
The chart list R-Values for different foam types, both thickness, and densities. Ideal™ Spa Covers use Expanded Polystyrene Foam (virtually every spa cover is made using this insulation). To calculate the R-Value of tapered foam, the average thickness of a 96″ x 96″ (8ft x 8ft) spa cover was used. If the size of your spa cover is smaller, the actual R-Value will be higher than stated in the chart. This is because the outer edge of the foam is cut to make your spa cover and the outer edge will actually be a bit thicker. (Example 8′ x 8′ (1.0 lb) spa cover the R-value is 13.2. Reduce the size of the spa cover to 7′ x 7′ and the R-Value increases to 13.55).
Typical Spa Cover R-Values (Based on a 96" × 96" Cover)
True R-values reflect the insulation foam only.
Although covering foam in marine vinyl can improve overall insulation performance, it should not be included in the advertised R-value.
| Foam Type | Density | Taper | Avg Thickness | True R-Value |
|---|---|---|---|---|
| Standard Foam | 1.0 lb | 4″ × 2″ | 3″ | R-10.5 |
| Deluxe Foam | 1.5 lb | 4″ × 2″ | 3″ | R-12 |
| Heavy Duty Foam | 2.0 lb | 4″ × 2″ | 3″ | R-12.6 |
| Super Foam | 2.0 lb | 5″ × 3″ | 4″ | R-16 |
Ideal™ spa covers are vacuum sealed in the proprietary VPB3000 vapor barrier and built with marine-grade vinyl to help preserve insulation performance over time.