Inner tank :SUS 304 Inner tank thickness:1.2mm Outer tank:SUS 304 Outer tank thickness:0.31 Insulation: Polyurethane imported from south korea Insulation thickness:50-65mm Frame: SUS430 Frame thickness:1.5mm Pressure parameter:0.6mpa Conducting materials: heat tube Advantages: For the pressured operation, Got more rushed hot water while bathing. Even one vacuum tube broken, the whole system can go on working