The term “Low E” means low emissivity. Emissivity is a property that’s unique to materials, such as glass, which light can freely pass through. Low E is a coating of non-visible, microscopic layers of silver sandwiched between layers of anti-reflective metal oxide coatings. Added to the surface of window and door glass, Low E provides greater energy efficiency, increased comfort and protection from damaging UV rays. By filtering out the part of the light spectrum that transmits heat, Low E reduces a window’s U-Value and increases its R-Value.