The manufacturer of our covers was the first to incorporate a  4" - 2-1/2"  tapered foam core, that allows water to run off much faster than the 3-1/2"- 2-1/2" cores most others use, and it adds extra strength to the center of the cover where it is needed most. There are 2 grades of foam core available, 1-1/2 lb which is standard, or as an option you can have a 2 lb core (a cover lifter may be necessary due to the added weight). The "Vapor Proof Barrier" is an exclusive state-of-the-art heat/vacuum sealing technique that is fully guaranteed against water absorption. The "Sure-Loc" locking fasteners meet and surpass strict ASTM approval for this type of mechanism. Additional features include heat sealing gaskets, lock & key-style safety straps, and a heavy duty marine grade vinyl. All of our spa covers are lift ready, for use with most any cover removal system on the market today. Remember, NEVER use Armor-All, or any automotive vinyl cleaner. They all contain alcohol and will eventually dry the vinyl out. We recommend cleaning with a mild detergent or saddle soap. There is a new protectant on the market,  "303", that is also highly recommended.