R-Value is mainly determined by the thickness and density of the core material. Other factors that contribute to the R-Value are the vinyl used and the poly wrap material that seals the foam core.
The core is made up of a Chlorofluorocarbon (CFC)-free foam that is moisture resistant, chemical resistant, and carries an insulation and compressive strength.
Examples of R-Value are:
1lb density tapered by 4” to 2” has an R-Value of 10.74. 2lb density tapered by 4” to 2” has an R-Value of 13.05
The vinyl and sealed core can typically add a R-2 value bringing the total R-Value of a 2 lb foam density to R-15
Don’t forget, a waterlogged hot tub cover can reduce the R-Value by up to 75%