solar thermal collector,25mm Hail Resistance Includes Vacuum Tubes, Heat Pipes, Manifold, Frame,Silica Gel. solar thermal collectorSpecifications: Manifold: Interior: red copper with 1.2mm thickness Exterior: aluminum alloy with 1.8mm thickness Maximum pressure: 12bar Coating of vacuum tube: SS-C/CU 3-high vacuum tubes Heat preservation: 72 hours Hail resistance: 25mm Insulation: polyurethane/ ...