The Invention of Insulated Glass Units

By nature, a single piece of glass has little resistance to either heat gain or loss, primarily because it is a good conductor and a very poor insulator. Recognising this problem, T.D. Stetson (USA) registered the patent for insulated glass in 1865. Stetson discovered that by adding a second panel of glass separated by still, dry air the insulating properties of glass could be improved. The improved performance of this insulated glass is attributed to the low thermal conductivity of the air pocket. It was not until after World War One that commercial production of the "bonded units" commenced, with manufacturing techniques improving throughout the 1950's in Europe and the USA.

Methods used to seal the unit have progressed over time from the original metal to metal, to metal soldered, then glass fused and finally, to the main current day process, the double sealed system.

The higher insulating effect (lower U value) provide by a Low E coating in a double glazed unit is due to the high reflectance of long wavelength radiation at ambient temperatures (Figure C).