• You can see the basic structure of a double-glazed window aboard an airplane.Jupiterimages/Goodshoot/Getty Images
  
  Double-glazed windows consist of two parallel panes of glass with a space between them. This space, which may simply contain air or may be filled with an insulating gas, serves as an insulating "cushion," helping to maintain the difference in temperature between indoors and out. Highly popular in cold climates, double-glazed windows come in a range of styles to fit every structural and decorative need.
  
  

Tinted Double-Glazed Windows

• Double-glazed windows are already exceptionally effective at keeping heat from escaping outward from a warm home to the cold air outside. If you live in a climate with relatively mild winters, you might also want your windows to keep the sunshine from heating up your home excessively during the summers, an effect known as "heat gain". To improve your summertime comfort, you can install double-glazed windows with tinting. Just keep in mind that the reduction in heat gain, while an asset in the summer, may force you to use more energy keeping your home warm during the winter months. Usually, tinted windows have a slight bronze or gray tint within the glass itself. In double-glazed windows, the outer glass is often bronze or gray and the inner pane is clear.
  
  

High-Performance Double-Glazed Windows

• Also known as spectrally selective tinted glass, high-performance glass is an improved variation on tinted glass, and is available for double-glazed windows. Like tinted windows, high-performance windows efficiently reduce solar heat gain, making interiors more comfortable during sunny, warm summer days. However, unlike the bronze or gray tinting on traditional tinted windows, high-performance windows usually have light blue or light green tinting, which allows a higher transmittance of visible light. As a result, the window allows just as much visible light to enter your home, helping to brighten it. However, this specialized tinting does not affect the window's U-value, which corresponds to its ability to insulate.
  
  

Gas-Filled Double-Glazed Windows

• Instead of filling the gap inside a double-glazed window with air, you can also install double-glazed windows that contain insulating gases, such as argon or krypton. These windows reduce the window's heat loss but permit higher solar gain. As a result, these windows ideally complement cold places where interiors require heating throughout the winter. By increasing the solar gain, these gas-filled windows produce a greenhouse effect, letting the maximum amount of solar light to enter the home and warm the indoor air. This also makes gas-filled double-glazed windows ideal for home designs that make use of passive solar heating. Depending on the degree of solar gain that the window permits, a gas-filled double-glazed window can have a U-factor of around .25 or .30, compared with factors of around .49 for regular double-glazed windows. The lower U-factor corresponds to an improved ability to insulate.