Low-E glass is short for Low Energy glass and was developed in 1983.
When solar rays hit building surfaces, they are converted into thermal energy (heat). During the colder months, we can benefit from the solar energy heating our houses.
Low-E glass is coated with a thin metal coating that allows solar rays to pass through, just like regular glass. However, once inside, the heat is reflected back into the room when hitting the inside of the window. This puts the solar energy to use heating the house.