Northwest Energy Savers:
Glass For Energy Efficient Windows

Low-e Glass -

is the term that is used most often when discussing energy efficient windows. It means Low Emissivity glass which refers to glass that has been specially treated to reflect heat. The technology originated with NASA. The same technology that is used for the glass on the astronauts' helmet is used on the windows in your home. Basically a thin coating of silver (as well as some other metals) is applied to one of the surfaces of the glass (usually the inside of the outside pane in the IG unit) through a process called "Sputtering". See illustration above of low e2 glass which has two coats of silver and 6 coats of other oxides, note all 8 coats are less than 100 thousandths of an inch thick. ( low e 3 glass is available with some manufacturers, even more energy efficient !) This process blocks the sun's heat from penetrating the window, resulting in a lower U-factor and SHGC number.(See previous discussion of this under What Makes a Window "Energy Efficient"?

For a more detailed explanation of Low -E glass go here www.cardinalcorp.comThe more you know about windows, the better you are able to make an intelligent decision, based upon facts, not sales hype.