How are double glazed units structured?
Double glazed glass have two panes of glass seperated by a layer of trapped air or Argon gas. The glass becomes well insulated so that little or no heat transfers between the glass. In addition to this, there is often a desiccant between the panes to absorb any stray moisture and stop fog from forming between them. The window or door glass can be clear or covered with a tinted or reflective coating.
Benefits of Double Glazing:
How does double glazing actually insulate?
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 millimetres thick, heat then can easily flow through them thus making it more expensive to heat and cool your house. Double glazed windows are designed to let in light while blocking the movement of heat, turning your windows into good insulators.
Window and door glass can insulate in different ways - having two panes of glass doubles the amount of glass that heat has to get through, slowing its movement from your house. The real insulation power comes from the trapped air as mentioned above. Heat is motion in molecules - the hotter a material is, the faster the molecules move. When excited molecules bang into nearby molecules they spread the heat generated. This is called conduction. Because air molecules spread out, they do not conduct nearly as well as a solid like glass. 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.