The idea behind double glazing is very simple, but can make a huge difference to the amout of energy wasted in a house, and also can make a huge difference to the cost of heating your home.
Double glazing is basically two panes of glass separated by a small layer of air. This reduces heat transfer across the windows, and makes them more efficient. The gas space between the panes of glass might just be air, or it might be another gas. The gas space is sealed to prevent the gas escaping, which prolongs the efficiency of the windows.
The thickness of the glass can also vary, with thicker glass being more efficient, but more expensive.
Because these windows are really two windows in one, double glazing repair can be costly and complicated, so it is best to take care of double glazed windows. Using a reputable company to fit the windows can also make a difference to the life of the windows.
Most new houses are now fitted with double glazing as standard, and this forms part of the energy efficiency rating of the house. As more older houses are retrofitted with energy saving devices, double glazing will continue to be the window of choice.