Low-E” literally means low emissivity, which in turn means a surface that emits low levels of radiant heat. All surfaces reflect, absorb, and transmit heat. So, a Low-E coating reduces the amount of that heat transfer. When talking about replacement windows the term Low-E really applies to the glass being used.Because it resists ultraviolet light, low-E glass prevents sunlight exposure from damaging carpets, draperies, sofas and other furnishings. Plus, low-E glass reduces sunlight glare in a room.The coatings reduce glare and reflect the sun's heat away from the structure. While windows with low-E glass generally cost 10 to 15 percent more than windows with standard glass, they can increase energy efficiency by 30 to 50 percent.