Our covers are made using only top quality materials on state of the art equipment. Our spa covers use 2 pound density virgin EPS foam core for insulation. The covers have an R-value of 19 for the 4" to 2" tapered 2 pound density foam. We also offer 5" to 3" tapered 2 pound density foam which has a higher top strength and better insulating properties with an R-value of 21. We use 28 ounce marine grade vinyl which features mildew inhibitors and UV stabilized coloring to help prevent fading. The double sided, solid cover liner we use is chemically treated on both sides to help prevent chemical damage.