2 lb. density, 1/4" thick closed cell foam. Because the foam is 'closed cell' it will not absorb water. Unlike other blankets, it's not necessary to coat the foam with a colored vinyl to keep the water out. By eliminating evaporation a floating cover can reduce the operating costs of a spa in numerous ways. Blankets over 5’ wide consist of two pieces of foam “welded” together. These blankets can be cut to size easily. Heat travels through moist air much quicker than dry air. Reducing the moisture between the water surface and your insulating cover will cut down greatly on heating costs.