A type of clear glass with a microscopic thin film of metal-oxide, low-emittance glass, also known as Low-E, is a recent energy saving tool to have entered the building construction industry. Glass normally has a high emissivity rate, i.e. it has a relatively high ability to absorb or emit energy in the form of radiation. The maximum amount of heat is lost or gained through windows, hence windows are known as the “thermal weak spots” in buildings. Low emission glass is used particularly for windows as it has a low heat emission rate, which means it can absorb or reflect heat and so offer insulation against cold and heat.