What’s The Difference Between Toughened, Tempered, & Laminated Glass?
Not all safety glass is the same. What’s the difference between toughened, heat-strengthened, and laminated glass? Read on to find out…
We could wax lyrically about glass. In fact, we regularly do.
In previous blog posts, we’ve highlighted its ability to provide us with beneficial natural light, its transformative characteristics when used as part of a home extension project, and its role in providing some of the most memorable moments in Hollywood history.
But despite its almost endless list of beneficial attributes, glass has one habit that has kept pioneering manufacturers busy since its first creation.
Thankfully, however, that’s not the end of the story.
Safety Glass, in a nutshell
Instead, we have safety glass: an umbrella term for several methods of significantly strengthening annealed glass using heat, chemicals, and additional materials. To learn more about the concept, we would recommend reading our guide to safety glass. It’s excellent. (But we would say that.)
Beneath that umbrella term are toughened and heat-strengthened glass, as well as laminated glass. The development of these products has opened the architectural door to a world of structural glazing possibilities.
For readers hoping to incorporate toughened, heat-strengthened or laminated glass into their next project – whether that’s as part of a curved glass structure, a swimming pool enclosure, or some other stylish feature – it’s important to understand how each product is made, its characteristics, what applications it is suitable for, and what applications it wouldn’t.
In doing so, we can then answer the question: what’s the difference between toughened, tempered, and laminated glass?
Let’s start with toughened and heat-strengthened glass.
What is toughened glass?
When glass is heated up to a temperature between 600 and 700 Celsius is becomes soft and at this stage it is then rapidly cooled (known as quenching). This puts the surface under compression. The process creates a highly compressed surface layer which can make the final product up to four or five times stronger than its original form. If it shatters, toughened glass has the ability to break into thousands of uniform cube-shaped pieces rather than sharp shards that could cause harm to those in the vicinity.
What practical uses does toughened glass have?
Toughened glass might sound most like the sort of requirement you’d need when building a bomb shelter, but it has plenty of architectural uses where the glass needs its own inherent strength but, should it get broken, will fail in a safe controlled manner. This includes areas where high concentration of load is expected, like with bolted or clamped connections or where high distributed loads are likely, for example, balustrades and floors.
There are certain critical locations where safety glass is a requirement, including all doors, or their side panels and where glass is close to the floor level. Toughened glass is particularly good at withstanding high temperatures or when there is a significant temperature difference over different parts of a piece of glass. Failure of this kind is called thermal cracking (or thermal shock) and is unlikely to happen in toughened glass
What is heat-strengthened glass?
Heat-strengthened glass is created in a very similar manner as toughened glass but at a lower temperature and a slower cooling time. This allows it to become around twice as strong as it was in its original form. Like its toughened sibling, it is unlikely to be affected by thermal cracking
What’s the difference between toughened and heat-strengthened glass?
The major differences in the two types of heat-treated glass is that toughened is about twice as strong and breaks into safe-sized pieces. Heat-strengthened glass therefore needs to be laminated should safety glass be required. Heat-strengthened glass breaks in a much more controlled manner, rather than explodes. Toughened glass is susceptible to failure through Nickel Sulphide inclusions where heat-strengthened glass is not.
What is laminate glass?
Laminated glass is created by sandwiching a laminate material – such as polyvinyl butyral (PVB) plastic – between two or more layers of glass. Laminated glass is considered to be a type of safety glass because when it breaks, it doesn’t shatter. Instead, the pieces remain bonded to the laminate material, and the glass is able to retain its overall structure.
This is called post-breakage behaviour and is important when considering what happens if, for example, somebody is standing on it at a substantial height (or if it’s suspended at a substantial height above somebody!) – such as an opening glass floor. Often toughened glass is laminated however much more likely is the use of heat-strengthened glass for laminated panels.
Glass in its standard annealed form can also be laminated although this would be considerably weaker and very susceptible to thermal cracking. Another advantage with laminated glass is that the interlayer materials will filter out approximately 99% of harmful UV light. It also works to reduce sound passing through.
What practical uses does laminated glass have?
Laminated glass is most commonly used in the production of car windshields where remaining in place even after breakage is of utmost importance. It is also regularly used in the architectural world as part of projects where the structural integrity of the glass mustn’t be compromised, even after a breakage or failure. This is often extended to cover security and anti-bandit screens.
Examples of where laminated glass could prove useful include:
- Glass walkways;
- Glass floors;
- Glass staircases;
- Glass balconies; and
- Opening glass roofs.
In short, laminated glass is useful for any part of a project where it would be dangerous for the glass to suddenly shatter and fall apart, whether into sharp shards or uniform cube-shaped pieces, as is the case with monolithic toughened glass (which you’ll already know if you’ve been paying attention!)
What does the future of strengthened glass look like?
To answer the question of what the future of strengthened glass looks like, we must first turn our attention to the past.
Francois Barthelemy Alfred Royer de la Bastie is the impressively named figure to whom the concept of strengthened glass is first attributed. In 1874 he patented the process of quenching molten glass in a vat of oil or grease, a method of tempering.
Before that date, however, glass was strengthened simply by making it thicker, which, in turn, made it heavier. Architects who wanted to use glass as anything more than a window would have to build a substantial skeletal system to support it.
Today, however, the need for a visible skeletal structure has been almost entirely removed as glass is far lighter and stronger than it was previously. Indeed, Cantifix built the World’s first frameless glass structure back in 1991 and has built plenty since – ensuring uninterrupted views of the outside world – to know that the future has clearly arrived.
As part of the future of strengthened glass, most experts expect to see developments in chemical strengthening, whereby small sodium ions in the glass’s surface are replaced by larger potassium ones, creating compression without relying on extreme heat. The days of using standard annealed glass are surely numbered and the future is firmly in the strengthened camp.
Monolithic Toughened versus laminated heat-strengthened glass. Which is better?
Laminated glass is undeniably the most effective type of safety glass available because it retains its form even after breaking. But laminated glass can also be far heavier and more expensive than a single pane of toughened glass, limiting its use to specific parts of your glazing ambitions rather than being used as a wholesale solution.
If we lived in a world which had no financial constraints, then all glass would be a lamination of adequately thick heat-strengthened glass – the perfect mixture of strength, safety and security. Regrettably budget constraints often mean making judgements about levels of safety, which can appear strange when put alongside decisions about the quality of the kitchen worktops.
Still not sure which type of safety glass is suitable for your project?