We have noticed a number of people entering our blog after searching to find out what a double-glazed window is. So, not wanting to disappoint we shall answer the question directly.
Double-glazed windows contain what is termed as a double-glazed unit, rather than a single sheet of glass. A double-glazed unit contains two panes of glass which are sandwiched together and held separate by a spacer bar that runs around the outside edge. The whole unit is sealed air tight with the cavity between the two panes often filled with an inert gas like Argon or Krypton to reduce the transfer of heat through the unit.
To offer further energy efficiency, double-glazed units often feature a special Low-E (low emissivity) coating on the inside pane and a Low Iron glass as the outside pane. These features help to reflect heat back into the home, while also controlling the amount of sunlight that can pass through the unit.