Low-emissive (Low-E) glass is window glass that has been treated with an invisible metal or metallic oxide coating, creating a surface that reflects heat, while allowing light to pass through. This energy-saving technology first became available in 1979 and continues to grow in popularity. Windows treated with Low-E coatings are proven to reduce energy consumption, decrease fading of fabrics, such as window treatments, and increase overall comfort in your home.

How Low-E Glass Works

The heat that passes through your window glass is measured by the U-factor or ultraviolet light. The lower the U-factor the more energy-efficient your glass is. This type of light is produced by the sun and generates heat in your home. Too much of this heat, especially during summer, can cause your air conditioning bill to go up in an effort to keep your house cool. Low-E glass reduces the amount of ultraviolet light that enters your home, without blocking visible light. Conversely, in winter, Low-E glass reduces the amount of heat lost through your windows from the inside of your home, keeping heating costs down. Depending on your home’s heating and cooling needs, various types of Low-E glass have been developed to allow for high, medium or low solar gain.

How Low-E Is Applied

In warmer climates, Low-E coating should be applied to the outside of window panes to keep the sun’s heat out. While in colder climates, Low-E coating should be applied to the inside of a pane of glass to keep heat trapped in. This way, radiant heat is kept on the same side of the glass from which it originated.

Window glass is treated with either a hard or soft Low-E coating. Soft Low-E coatings are known to have a limited shelf life and need to be carefully applied to insulated multipane windows to keep them from being damaged by air and moisture. Hard Low-E coatings are more durable and are a better choice for individuals who wish to apply a Low-E coating to their windows after they’ve been manufactured. Low-E films are also available, and easy to apply, for those who wish to enhance their windows on their own.

Source: http://www.lowes.com/cd_The+Benefits+of+Low+e+Glass_1277235128_