... good heat preservation effect, the heat exchanger choose SUS304 stainless steel production, anti-corrosion, not deformation, thermal insulation ... galvanized/ co lour steel, 0.31mmFrame: galvanized steel/stainless steel SUS304/aluminum alloy, 1.5mmInsulation: polyurethane frothing, 50mmVacuum tube: AL/N coating ... , consumer can enjoy comfortable bathe anytime. Stainless Steel Summer Solar Water Heater