Low-emissivity glass (or low-e glass) is a transparent double or triple glass, to which an invisible metallic layer has been added, which allows exterior light to pass through but blocks radiant heat coming from inside the home. Low-emissivity glass may be used with argon gas. The main benefit of low-E glass is that it decreases energy costs. This insulating glass not only cuts heating costs in winter, it also lessens the amount of solar heat in summer, which reduces the need for air conditioning.