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, ISO900:2000, CE certificate;3, 0.91 transmittance of outer tube4, The outer tube is made of extremely strong transparent quartz sand which can resist impact from hail up to 25mm in diameter.5, The inner tube is also made ...