Understanding Window Glass Options

Windows are one of the biggest factors in a building’s energy efficiency. Understand how to choose the best glass for your needs here.

Understanding Window Glass Options

Before you buy or replace your windows, it’s important to understand the different types of window glass available. Most people when looking at new or replacement windows, consider the frame material, and other design aspects, rather than thinking about the glass itself. In this article, we will help you understand the different types of glass available, and their benefits and shortcomings.

Windows are one of the biggest factors in a building’s energy efficiency, with heat loss and gain through windows, a major contributor to your energy costs. Here at Complete Film Solutions, we have taken an in-depth look at the benefits of high-performance window film to improve window energy efficiency. Check out our article on how window film can significantly improve your window efficiency, for further details on the best and most cost-effective option to improve window performance.

If you have been considering installing window film to your windows, it is important to understand the different glass types, as not all glass types are compatible with all film types. If you do not know what type of glass you have, it is important that your glass is analysed at the time of the quote, to ensure that the correct film is installed for your glass type. Many film installers will have glass analysis tools that can be used to identify glass types where it is not known.

What is Double & Triple Glazed Glass?

Common glazing terminology provides information on the number of panes which sit within the window frame. Single glazing refers to one pane of glass in the frame. Double glazing indicates that the window frame has two panes of glass, separated by a spacer. Triple glazing has three panes of glass attached to a spacer within the frame. These double and triple glazed windows are also sometimes known as thermal windows or Insulated Glass Units (IGUs).

With window efficiency taking a front seat in most home and corporate building designs, double glazing is soaring in popularity. Some buildings are now even being built with triple glazing!

Double glazing has 4 surfaces:

  • Surface 1: The outermost surface of the outermost panel of the double-glazed unit – ie the side that is on the outside of the home and is exposed to the weather.
  • Surface 2: The internal or opposite side of Surface 1 – ie the internal facing side of the outermost panel of glass.  It forms one side of the sealed gap in the double-glazed unit.
  • Surface 3: The outside-facing side of the innermost panel of the double-glazed unit.  It forms the other side of the sealed gap in the double-glazed unit.
  • Surface 4: The inside facing side of the innermost panel of the double-glazed unit – ie the side of the glass that is on the inside of the home.

Double Glazing Surface Numbers

Within double glazing, there is a wide variation in types of double glazing available, based on the following factors, all which impact on the overall performance (and cost) of the IGU:

  • Frame material – steel, aluminium, timber, PVC (Timber and PVC frames will result in higher energy efficiency than steel or aluminium frames, as they are better thermal insulators than high conduction metal frames)
  • Glass type – toughened, laminated, low-e glass, tinted glass
  • Glass thickness
  • Width of the gap between the glass panels
  • Whether the gap between the panels of glass is filled with air or gas. If it is gas-filled, this is most commonly Argon gas – a clear, odourless, non-toxic gas that is less conductive than normal air, helping to prevent or slow down heat transfer through the glass.  Gas-filled spaces thus improve the energy efficiency of the IGU
  • Construction of the IGU – eg constructed as a sealed unit, requiring removal of existing windows to install, versus a “retrofit” option, where additional glass and hardware is added to existing window frames and glass (sometimes using magnets, double-sided tape or silicone) -which will be a lower performance, lower-cost option.

Double glazing enjoys an excellent reputation for reducing heat loss through windows in winter and reducing noise transmission through the glass. While it does reduce heat transmission through the glass in Summer compared to single glazing, it often requires additional features such as low-e glass on Surface 2 or an external window solar film to enhance its performance against the intensity of Perth heat on Northern and Western elevations.

What is Low-E Glass?

Low-e glazing stands for “low emissivity”. Normal glass is a high conductor of heat – i.e it releases a lot of heat into the surrounding space. This heat release results in unwanted additional heat gain in warmer months, and undesirable heat loss during winter. Low-e glass is specifically designed to release less heat energy and slow the rate at which heat transfers through the glass.

It is created when a low-e coating is fused onto the internal-facing surface of the glass during manufacture. Any glass type can be made low-e during the manufacturing stage, whether it is float glass, laminated glass or toughened glass.

The coating is nearly invisible (although anecdotally, there have been reports that the low-e coating can cause a somewhat hazy appearance to glass). The coating does need to be exposed to air or a gas-filled space to be effective. It is for this reason, that window film should never be installed to low-e glass. By installing window film to low-e glass, the low e coating is no longer exposed, and will no longer be effective. Window film should only be applied to the external surface of low-e glass, where there is no coating.

Sometimes, people are confused and think that when laminated glass is manufactured to have low-e properties, that the low-e surface is on the film interlayer between the two panels of glass. This is not the case. The Low E surface is ALWAYS on the internal-facing surface, where it is exposed to air (or gas in the case of a gas-filled IGU).

What is Laminated Glass?

Laminated glass consists of two or more layers of glass with a film interlayer between the layers. The glass panels and film interlayer are bonded as one strong unit with the application of heat and pressure. It is designed to be a safety glass, as when it is broken, the glass particles tend to adhere to the film, providing increased protection (compared to toughened or float glass) from flying or falling glass fragments. It is typically a stronger glass than either float or toughened glass, and may deter break-ins, although the film interlayer is not, strictly, a security film. Applying a security window film to glass is still the best option to prevent illegal entry to your home.

Laminated glass is not compatible with all forms of window film. Any solar films that are dark (typically, any window films less than 40% visible light transmission, and dark in colour) are not recommended for laminated glass. This is because the darkness of the film creates a heat absorption effect. This can interact with the film interlayer in the laminated glass and be a contributing factor for thermal stress.  A silver finish film is the exception to the rule – this may be lower than 40% visible light transmission, but because it is a very high reflective film (as in like a mirror), the absorption effect is not created like it is with dark films.

Laminated glass is suitable for any location in the home where a safety glass is required – such as wet areas, windows adjacent to outdoor pool areas, or any full-height glass windows or doors, where there is potential for a person to walk into the glass, not realising that it is a window. If you have young children and low light windows in your home (or windows next to beds/ cots), laminated glass also provides peace of mind that your child would be less likely to sustain an injury if their play caused them to fall against the glass.

There are also forms of laminated glass that have been shown to help reduce noise transmission, so you may consider laminated glass for any windows impacted by external noise.  This would be a more cost-effective glass replacement option to address noise issues than double glazing.

What is Toughened Glass?

Toughened glass (or sometimes also called tempered glass) is another option for safety glass (and is typically used in all the same applications as laminated glass listed above), as it designed not to shatter on impact, rather it will crumble into less hazardous pieces. Toughened glass is created by subjecting normal glass to a heat-treating process to increase its strength, followed by a cooling process.  This process means that it is approximately 4 times stronger than float glass, but is otherwise identical in colour, clarity and light transmission from the original glass product.

That said, while toughened glass is stronger than float glass, toughened glass panels are still very susceptible to break-in, and can be broken relatively easily and quietly compared to float glass, as demonstrated in our video.  Due to how toughened glass breaks into small fragments, additional measures (most commonly Ultraflex Bonding – see picture below) are needed when applying security window film to toughened glass panels, to ensure that the film, glass and frame are one strong unit to prevent illegal entry.

Ultraflex Bonding in a Window Frame

What is Float Glass?

Float glass (or sometimes also called Annealed glass) is the most common glass seen in Australian homes. It is manufactured by pouring molten glass from a furnace to a large bed of molten tin. The glass “floats” on the tin (hence the name), spreading and seeking a controlled level surface. It slowly solidifies, before moving through a cooling process in a temperature-controlled glass kiln, over more than one hundred metres long. This creates a continuous ribbon of glass up to 6m wide at room temperature.

Float glass is available in a range of different thicknesses. Some float glass in older homes (pre 1990s) may only be 3mm thick, which presents a significant safety risk, as it would break very easily if subjected to a relatively minor force (even from a stone flicking up from a lawnmower for example). Float glass breaks into very sharp shards, which can cause a significant and potentially life-threatening injury.  Current building guidelines in Australia dictate that all glass in residential homes must be a minimum of 4mm thickness. Any full height glass that could be mistaken for an opening must be glazed with safety glass, such as laminated or toughened glass to reduce the risk of injury.

What is Tinted Glass?

Most glass options now also have the option of being manufactured with a built-in tint – i.e the glass itself is coloured with a tint, rather than applying a tint film. This can be very effective at reducing glare and providing privacy, however, typically does not provide significant benefit in heat rejection. A dedicated solar film applied to clear glass will always outperform a tinted glass option.

Installing 3M Window Films

3M’s extensive range of Solar and Low-E/ Insulating Window Films are a proven, cost-effective option, to improve window energy efficiency. Check out our recent Case Study on new home builds, and how installing 3M Thinsulate low-e window film was an excellent option for improved performance.

3M Safety and Security Films can offer solutions to deter illegal entry to your home, or provide peace of mind to upgrade older, thinner glass to meet current Australian Standards, to protect your family from accidental injury.

Speak to an expert at Complete Film Solutions, for advice on choosing the best window film option for your home or commercial space.

Contact Complete Film Solutions Today

Choosing the right type of glass for your new or replacement windows, can have a huge impact on your home’s aesthetic appeal, sound insulation, energy efficiency, and overall comfort. Our glass glazier has over 30 years’ experience in the industry and will help you choose the right glass for your windows. To arrange a free quote, please call the Complete Film Solutions team on (08) 9330 2322, send an email to email@cfsols.com.au, or submit an enquiry today!



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