R-Values are nothing more than a materials ability to resist the conduction of heat flow thru a solid. To help consumers compare the R-Values of different types of insulation, standards were developed for industries to follow when referring to their products. To help educate you for your next cover purchase, here is some background information:
1) Manufacturers are only allowed to state the insulating value of the insulation. In the case of hot tub covers, the R-Value advertised should only be for the foam itself. Although it is true that the layer of polyurethane and the marine vinyl will increase the R-Value, it is not supposed to be included.
2) The R-Value of insulation will increase as the air temperature on the cold side of the insulation decreases. In other words, if you test insulation at 25°F and then at 10°F, you will get a higher R-Value at 10°F. ASTM has not specified a temperature that hot tub covers must be tested at, however, the air temperature must be disclosed when an R-Value is stated. This helps consumers compare apples to apples and also preserves the integrity of our industry. We have included a few different temperatures in our chart below so that you can see the difference that air temperature makes.
The following chart list R-Values for different thicknesses and densities of Expanded Polystyrene Foam (99 % of foam covers use this insulation). For tapered covers, to calculate the R-Value we use the average thickness of an 8 foot by 8 foot cover. If your spa is smaller than 8 feet by 8 feet, your average will be thicker because the outside edge of the foam is cut off to make your cover. Therefore, your cover will actually have a higher R-Value than the table lists.
|Outdoor Temp.|| 1.0 lb foam |
| 1.5 lb foam |
| 2.0 lb foam |
| 2.0 lb foam |
|-4°C||R 12.6||R 13.8||R 18.4||R 23.7|
|4.4°C||R 12.0||R 13.2||R 17.6||R 22.6|
|24°C||R 10.8||R 12.0||R 16||R 20.6|
Our 4" to 3", 2.0 lb foam covers have an R-Value of approximately 18.4 at 25°F, for the foam alone. All of our covers have the foam cores heat sealed in polyurethane, use the best marine vinyl, have vapor skirts and our hinges have small pillows that compress when you close the cover to prevent heat loss from the hinge. All of these characteristics increase the insulating value of the cover beyond the value of 18.4.
We hope that this short article has taught you a little bit about R-Values and the next time you see an R-Value that seems a little to good to be true, you now have enough background information to ask some intelligent questions!