Simply Stated: The R-values Are A Measurement Of The Materials (Foam Panels In Spa Covers) Ability To Resist The Conduction Of Heat Flow Through A Solid (Loss Of Heat)
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).