What Double Glazed Windows Are Used For

• Windows are designed to let in light, while blocking air and objects from entering the house. In addition, windows provide some insulation, but not much. Windows are only a few millimeters thick, and heat can easily flow through them, making it more expensive to heat and cool your house. Double glazed windows are designed to let light through while blocking the movement of heat, turning your windows into good insulators.
  
  

How Double Glazed Windows Are Structured

• Double glazed windows have two panes of glass separated by a layer of trapped air. The space between the windows is very well insulated so that little or no air can leak between the panes of glass. In addition, there is often a desiccant between the panes to absorb any stray moisture and stop fog from forming between them. The windows can be clear or covered with a tinted or reflective coating.
  
  

How Double Glazed Windows Insulate

• Double glazed windows insulate in a few different ways. Having two panes of glass doubles the amount of glass that heat has to get through, slowing its movement and aiding insulation. The real insulating power, however, comes from the trapped air. Heat is motion in molecules--the hotter a material is, the faster its molecules move. When excited molecules bang into nearby molecules, they spread the heat. This is called conduction. Because air molecules are spread out, they do not conduct nearly as well as a solid like gas. As a result, the trapped air acts as an insulator. Some heat can still flow through the air, but it moves much more slowly than it does through glass.
  
  

Double Glazing Coatings

• Double glazed windows can also be improved by adding coatings. Different coatings are used for different purposes. For example, a reflective metallic coating on the outside of the outer pane will stop infrared radiation from passing through the glass from the outside, preventing the sun from heating the room. The same coating on the outside of the inner pane, however, will stop infrared from leaving the room, keeping it warmer. Double glazed windows can also be tinted to reduce the light coming in, just like normal windows.