Low-E varies from normal clear glass in that one side of the glass has a special metal coating, technically known as a low emissivity, or Low-E. Low-E coatings have been developed to minimize the amount of ultraviolet and infrared light that can pass through glass without compromising the amount of visible light that is transmitted. Therefore, Low-E glass is a type of insulating glass, which increases the energy efficiency of windows by reducing the transfer of heat or cold through glass, meaning in the winter your house stays warmer, and in the summer it stays cooler. There are two types of Low-E glass available: hard coat Low-E (pyrolytic glass) and soft coat Low-E, or sputter coating.