Completely Stainless Steel material used for rust-free longer life. Best quality Stainless Steel- corrosion-resistant SS304 used for the inner tank. High-quality three-target vacuum tubes for better efficiency. Polyurethane foaming Insulation used to prevent heat loss. Argon Arc welding used to Inlet and outlet, air vents and drain outlet. Electric heating rod with thermostat included for cloudy weather. Additional drain outlet for tank cleaning.