Low-E is the clear low-emissivity coating on one side of the glass that is microscopically thin and has optically transparent layers of silver sandwiched between layers of metal oxide coatings. Low-E filters the suns energy in the summer by reducing the amount of heat transferring through the window and reduces heat loss in the winter. Low-E lets in visible sunlight while blocking infrared and ultraviolet solar energy that fades carpet and furniture.