This HS303 Premium Hard-Side Waterbed Mattress is part of our Hydro-Support 300 Series featuring a deep molded feathertop pressure reduction surface for the greatest conforming comfort, heater-compatible bottom, bottom seams for greater durability, reinforced corners, 25 mil vinyl (25% thicker than most). The deeply molded feathertop surface provides reduced surface tension and no pressure points for the greatest comfort and best sleep. The HS303 is a Semi-Waveless waterbed mattress with 3 layers of internal full-body support fiber for significant wave reduction.