1,Solar vacuum tube for solar energy water heater 2,ISO,CE 3,Available ... in various size 4.5days delivery 5.OEM available 1, Vacuum tube is consists of two layer of glass tubes2, ISO900 ... ;3, 0.91 transmittance of outer tube4, The outer tube is made of extremely strong transparent quartz sand which can ... from hail up to 25mm in diameter.5, The inner tube is also made of quartz sand, but it is ...