Thermopane insulated window glass was invented by C.D. Haven in the United States in 1930. It is two sheets of glass that are bonded together in such a manner that they enclose a captive air space in between. Often this space is filled with an inert gas that increases the insulating quality of the window. Glass, in general, is also one of the best transparent materials because it allows the short wavelengths of solar radiation to pass through it, but prohibits nearly all of the long waves of reflected radiation from passing back through it.