How Double Glazing Works

What is double glazing?

Double Glazing

In the past, windows have been constructed with one single pane of glass only. Because single glazed windows are only a few millimetres thick, they serve as poor insulators - meaning it is easy for heat and cool air to pass through them. Today, double glazing is a more energy efficient solution that consists of two panes of glass with an air gap in between. The combination of two panes of glass and a locked air gap turn the windows into strong insulators rather than energy drains. The width of the two panes of glass and the air gap vary depending on the needs of the climate, exposure to the elements and orientation of the windows to the sun.

Some older windows can be retrofitted with double glazing, however today most double glazing units are manufactured as one single unit. The two panes of glass are sealed together and inserted just as a single pane of glass would be.

The sealed air gap between the glass improves insulation performance, which greatly reduces both heat flow and thermal conductivity through the window.

Benefits of double glazing

Double Glazing Benefits

Double glazing the windows and doors in your home will save you energy, money and improve comfort year round.

  • Added insulation
  • Reduced solar heat gain
  • Minimises heat flow between the outside and inside of your home
  • Reduces noise pollution without obstructing the view
  • Retains natural light flow into your home

How does double glazing work?


The sealed air gap between the two panes of glass significantly improves the insulation performance of the window. This gap acts as a buffer for the difference in temperature outside and inside the home.

Solar heat gain, which is the heat created inside your home when sun rays heat up a window, is greatly reduced with double glazing, as the outside pane of glass absorbs some of the heat, and reflects the rest back out. At the same time, the air gap between the two panes of glass stops this heat from moving through the glass inside. This makes double glazed windows more energy efficient - especially during the summer months, when the sun’s rays are much harsher, while keeping a cool and consistent temperature inside as a priority.

Thermal conductivity, or the flow of heat through glass, occurs when there is a difference in temperature on either side of the glass. In a well insulated home this makes it hotter outside in summer, and warmer inside in winter. Heat flow is when this heat escapes in winter, meaning you need more powerful heating to keep your home at a comfortable temperature. In summer, this heat leaks in from the outside, making your air conditioning work harder. The improved insulation performance of double glazing works to minimise the heat flow through glass. By stopping the heat at the first pane of glass and reflecting it back - either retaining the heat inside during winter, or reflecting it back outside during summer, it helps maintain a constant temperature in your home.

How do double glazed windows insulate?


The unique combination of dual glass panes and air make double glazed windows an energy saver rather than an energy drain.

More glass = better insulation

Because double glazed windows have two panes of glass instead of one, it is difficult for heat to pass through. The thicker the glass heat has to try to pass through, the better at insulating it is.

Trapped air = better insulation

The air locked between the two panes of glass in a double glazing unit is the main source of insulation. When a material is hot, its molecules move quickly, spreading the heat. Air molecules are spread out, meaning they cannot spread the heat as quickly as in a solid mass, like glass or timber. Because this air gap slows down the movement of heat through the window, it acts as a very good insulator.

Are all double glazed windows the same?

Double glazed windows come in a range of variations, suited to different climates, exposure to the elements and budgets. For more product information visit our FAQS page.

Double Glazing

Standard double glazing

Standard double glazing is simply two panes of clear glass with an air pocket in between. This double glazing uses the air gap to insulate, reducing heat flow and solar heat gain in your home.

Click here to read more about our Double Glazing

Smart Glass

The energy efficiency and effectiveness of double glazing can be improved with the use of low emissivity (Low E) SmartGlass. SmartGlass has a protective anti glare film which reflects harsh sunlight away from the window, reducing solar heat through the window. During the cooler months, this film reflects the warm air inside your home back in, rather than letting it drain through to the outside.



Thermal Glazing

In extreme climates, and climates with highly variable temperatures, Thermal Glazing is even more energy efficient. Thermal glazing uses low emissivity glass panes in either a double or triple glazing unit. Thermal glazing is the most energy efficient glazing option available, reducing solar heat gain and heat flow up to 68% more than standard single glazing.

Click here to read more about our Thermal Glazing

Will I get condensation between double glazing?

In double glazed windows, the space between the two panes of glass is usually fitted with a desiccant to absorb any moisture. The desiccant works by soaking up moisture to prevent any fog or condensation from forming on the inside of the two panes of glass. At Southside Aluminium Windows we use Viridian Glass, who provide high quality double and thermal glazing units, all fitted with a desiccant to combat condensation.

Window care and maintenance
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