About R-values and "fuzzy math"
R-value is a measurement of the heat resistance of specific materials like the fiberglass insulation in your house walls or the insulating foam in our cover. Theoretically, the higher the R-value, the better the heat retention and heat retention is a primary function of a good spa cover.
Most industries advertising R-value are regulated by FTC (Federal Trade Commission) standards. So for example, your home insulation must pass independent tests created by American Standards and Testing Methods (ASTM) in order to be advertised or marked with their R-Value. Unfortunately, there is no FTC-recognized independent test for spa covers so any R-value stated by a spa cover company is actually an unregulated, unmonitored "interpretation" of the numbers. We choose not to get involved in this kind of speculation as it is open to abuse, so we state only the known R-value of the insulation itself plus a small increment for the vinyl and the core wrap and leave the speculative stuff alone (additional R-value of the air space between the water and the cover, the space between the vinyl and the cover insulation, etc.). The R-value of the actual foam insulation plus covering in our Standard 1.5 lb foam covers is approximately 13.5 and for the Deluxe denser 2 lb foam, it's approximately 15 (based on an average insulation thickness of 3"). That's about the same as a typical outside house wall.
Despite questionable claims to the contrary, we can tell you this: our spa covers have the same or better R-value than any other spa covers sold at anywhere near our price. If you have any further questions about R-value or anything else about our custom spa covers, please contact us.