Laminated Glass Explained

For security reasons, glass that is difficult to pierce offers protection against forced entry or attack. For safety reasons, glass that holds together after breaking avoids the danger of piercing from shards of glass or falling shards of glass from above.

Laminated glass offers many benefits from safety and security to UV resistance and noise reduction.

What Is Laminated Glass?

Laminated glass comprises two layers of glass with an interlayer fused together by heating. The different layers are called plies and the interlayer can be a variety of plastic or resin materials. The cheapest and most popular ply used for domestic laminated glass is polyvinyl butyral (PVB).

The main uses for laminated glass are security and safety.

The laminated glass interlayer is difficult to pierce. Different interlayer materials are used for different purposes and security testing will test the glass against manual attack, including using an axe.

The unique quality of laminated glass is that if it breaks, the glass is fused to the PVB interlayer and stays in place. For this reason, it's used in skylights or glass ceilings to avoid glass shattering and falling from above.

Laminated glass is also used for car windshields and the cockpits of aeroplanes to avoid the glass being sprayed into the face and eyes if the windscreen should shatter at speed.

How Is Laminated Glass Made?

Laminated glass is made by fusing together plies of glass and interlayers to create a single sheet. For domestic windows, laminated glass usually comprises two plies of annealed glass and a ply of PVB for the interlayer.

Laminated glass can be manufactured in many ways for differences in the final product:

• Glass used (standard annealed, toughened)
• Thickness and number of plies
• The interlayer material (PVB is the most popular)
• Special coatings on the piles (i.e. for solar gain)

For security purposes, the glass can be made in different thicknesses with different interlayers specifically for either:

• Bullet resistance
• Forced entry resistance
• Blast resistance

The layers or plies are assembled together in a controlled environment and vacuum extraction removes the air between the layers. The sheet is heat treated, compressed and then placed in an autoclave before final inspection.

The PVB interlayer used for domestic laminated glass is made in multiples of 0.38mm with standard thickness being 0.76mm and 1.52mm.

For non-domestic uses, the glass can be made from multiples of plies with different types of interlayer material in different thicknesses. For example, the cockpit of an aeroplane has five plies fused together and the interlayer ply is 2.6mm thick compared to 0.38 of a standard domestic window. Bulletproof glass has a polyurethane interlayer 1.25mm thick.

The different interlayers all have their own unique properties and are used for different end uses of laminated glass:

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At Everest, we have two types of laminated glass

Which Is Stronger Toughened or Laminated Glass?

Laminated glass and toughened glass have their own unique properties and use. They are often confused, but they are two very different products.

Toughened glass is heat treated to be four/five times as strong as standard annealed glass. To compare laminated glass against toughened glass in a strength test based on breaking point, toughened glass is stronger. But, once it breaks, it will break into small granular pieces.

Once laminated glass breaks, it is held together on its PVB interlayer and stays in place. It's very difficult to pierce through laminated glass because of the PVB core. Effectively, laminated glass can be considered stronger overall, but in a different way.

When choosing between laminated and toughened glass you have to consider how the glass will be used and what is the predominant safety issue.

For security reasons, laminated glass is by far the superior product, especially for manual or forced attack. The interlayer will hold the glass together under exceptional circumstances and is used for jewellers' windows or bulletproof car windows to avoid penetration.

Where there is a danger of falling glass from overhead skylights or balustrades, laminated glass must be used.

In a domestic window, toughened glass is more resistant to actually breaking but it will shatter into small granular pieces to avoid injury. If security is not an issue, toughened glass is better for glazing in critical areas.

It's also possible to combine toughened and laminated glass for a glazing product that has a high breaking point and is difficult to pierce. This would be ideal for a glazed external door, where safety and security are both important.

Note that both laminated glass and toughened glass can meet safety requirements for glazing in critical areas.

How Laminated Glass Works for Sound Reduction

Laminated glass is used in noise reduction windows as it helps to dampen the sound.

Noise reduction windows can reduce soundwaves because they have a gap between the panes of glass filled with Argon gas that reduces the transmission of the wave.

By using a laminated layer on one pane of glass in the double-glazed unit, the panes have different widths and this is enough to cause the panes to oscillate at different vibrations.

The difference in frequency disrupts the soundwave and reduces the transference of noise through the glass. The PVB laminated layer can also dampen the sound transference through the pane of glass.

All of these factors combined can help to reduce noise by up to 40 dB.

How Laminated Glass Works for UV Resistance

Laminated glass also has the benefit of reducing UV light transmission.

UV bleaching is also known as colour fading or photodegradation, where ultraviolet light causes a change in molecular structure that reduces pigment.

Sunlight, as warming and uplifting as it is, can cause damage to fabrics, furnishings and floors where the intense light shines. Wooden floors can warp, leather settees crack and artwork can fade. This is especially a problem for windows that face south or southwest and are exposed to sunlight at its most intense during the day.

The PVB layer in laminated glass does reduce UV transmittance considerably compared to standard glass and helps to protect furniture and furnishings.

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It's worth noting that for valuable paintings or antiques, they can still be susceptible to even normal levels of daylight. In cases of precious artworks, they should be stored in darkness away from normal light.

The Benefits of Laminated Glass

Security

The main benefit of laminate glass is the additional security it provides to the window.

If laminated glass is broken, it's difficult to pierce and gain entry because the PVB layer acts as a barrier.

Laminated glass can withstand repeated blows from bricks or hammers. This resistance will either prevent or slow down gaining entry and help to prevent a burglary or vandalism attempt.

Laminated glass is useful for glazed external doors and for windows in secluded areas that might be vulnerable to break-ins.

UV Protection

The PVB interlayer will reduce UV transmission to stop the damage to furnishings and furniture, especially in south-facing windows.

Noise Reduction

Laminated glass can help with noise reduction because the interlayer disrupts sound waves as they pass through the glass. Sound can be reduced by up to 40dB which has the effect of seeming to move the sound further away.

Safety

In domestic properties, laminated glass will protect adults, children and pets from damage if a glazed door should break from impact.

Laminated Glass Uses

As mentioned above, the main benefits of laminated glass are the resistance to intrusion and that it holds together when broken.

Laminated glass is more expensive than toughened glass, but has more properties and uses. Laminated glass can be made with toughened glass plies for extra safety and security combined.

The main areas for the use of laminated glass are:

• Glass stairs and balustrades, for safety and strength
• Glass floors, for safety, so a floor doesn't just crack and give way
• Shop fronts, for security against theft from the window
• Aquariums and animal enclosures, for the safety of the animals and also to avoid escape
• Jewellery display cases, for security against theft
• Windscreens, to avoid glass sprayed in the face when driving
• Windows for UV resistance to protect furnishings
• Glazed entrance doors, for security and safety

How to Tell If Glass Is Laminated

As the laminate layer is so thin, unless you have a trained expert eye, it's difficult to detect any perceptible difference in the glass. The only way to see the PVB layer is at the edge of the glass, but that would usually be hidden in a glazed unit.

The easiest way to identify laminated glass is by the Kitemark if the glass has been branded.

Laminated Glass Security Credentials

Laminated glass can qualify as safety glass for building regulation purposes where glazing is installed in 'critical locations' if it carries a British Standard.

The most common British Standard classifications are:

BS EN 14449 Glass in a building – Laminated glass and laminated safety glass: Evaluation of conformity/Product standard

For glass to be considered 'safety' or 'security' glass it must also pass an impact or a manual attack test.

Read more about safety and security credentials and testing...

BS EN 356:2000 Glass in a building – Security glazing: Testing and classification of resistance against manual attack

The test measures how resistant the glass is to an attack using a hard body drop test and a manual attack using a hammer and an axe.

The security test is designed to demonstrate that the glass is resistant to manual attack. The first part of the test involves an impact test where a load of 4.11kg is dropped on the glass. The second part involves a manual attack with an axe.