The pontoons are filled with polystyrene. The plastic pontoons and plastic sheet is all lighter than water. The buoyancy factor is second to none. Other so called stable crafts have what appear to be pontoons from the outside but they are open. AquaTruck are a real pontoon based boat. Our CE certified 8.8m Aft Cab workboat is certified for commercial use 50 nautical miles offshore in Queensland. This is a testament to the buoyancy and safety that is inherent in these boats With a lighter than water material and sealed pontoons….it is hard to figure out how to sink them.