Low Emissivity glass is produced by vacuum sputtering technology. Emissivity measures the material's ability to radiate energy. As silver is the material with the lowest emissivity, one, two or three transparent layers of silver are applied on the surface of the glass for reducing the glass emissivity.
Combination of silver coating and several layers of optical coating can further improve visible light transmittance and reduce infrared transmission and solar heat gain. Clear float glass has an emissivity of approximately 0.85 that means more than 90% of absorbed heat is emitted from the surface. Applying low emissivity coating on the surface of the glass reduces the surface emissivity to less than 0.1. As low-E coatings reflect long wave IR, it reduces heat gain or loss in a building by redirecting the heat energy, so it ensures warmth in the winter and coolness in the summer