*** IMPORTANT ***This cover has a compartment directly under the reversible cover for you to have the ability to insert any combination of foam layers you want. The compartment is 4.5" inches. For example: You can purchase a 2.5" of high density foam and a 2" Layer of memory foam or latex foam. Or, 1.5" of convoluted foam and a 3" Layer of memory foam or latex foam. You can design your own.We highly recommend that you purchase the foam inserts at Overstock.comThere are two sets of zippers on this cover. The top zipper allows you to remove the summer / winter reversible cover. This will reveal the 4.5 inch European Duvet Compartment. The second set of zippers will reveal the inside of the cover where you will use your existing foam rails and waterbed mattress system.