Product Name Pressurized Pre-heated solar water heater Model YYJ-P01 Circulation Type Other Heating SystemThermosyphon (Passive) Connection TypeDirect-Plug Material Inner tank:SUS304-2B food grade stainless steel with thickness 0.4mm/0.5mm Outer tank:Galvanized steel -0.4mm / Aluminum-zinc coated steel-0.45mm Heat exchanger:Red copper coil with thickness 1.2mm Insulation:Polyurethane Foam - 50mm Frame:Galvanized steel -1.5mm/Aluminium alloy Vacuum tube:Cu-S/S-N/AL coating,47-1500/58-1800mm http://www.ejiasolar.com/