Laminated vs toughened safety glass: what's the difference?

Laminated and toughened glass are both sold as safety glass, and both are a big step up from the ordinary float glass in most older windows. They earn the name in completely different ways, though, and that difference decides where each one belongs. Here is how each is made, how each behaves when it breaks, and which to choose for doors, windows and shopfronts.

How toughened glass is made

Toughened glass, also called tempered glass, starts as ordinary float glass that is cut to its final size first. The edges are finished and any holes or notches are made, and then the pane goes into a furnace and is heated until it is close to softening. As it comes out, jets of cold air cool both faces very quickly. The outer surfaces set hard while the core is still hot, and as the core cools and shrinks it pulls the surfaces into compression.

That locked-in stress makes the glass several times stronger than float glass of the same thickness, and far more resistant to heat. It is also why toughened glass cannot be cut, drilled or trimmed afterwards: every size and every hole has to be right before the pane goes into the furnace. A toughened pane is always made to order.

How laminated glass is made

Laminated glass is a sandwich. Two or more sheets of glass are bonded together with a clear plastic interlayer between them, usually PVB (polyvinyl butyral). The layers are pressed together and heated so that the interlayer grips the glass on both sides and turns completely clear.

The glass itself is not made any stronger by this. What changes is what happens when it breaks. Our article on laminated safety glass and the PVB interlayer goes deeper into what the interlayer does.

How each one breaks

This is the real difference between the two.

• Toughened glass shatters all at once into small, blunt, cube-like pieces. They are far less likely to cause a serious cut than the long shards of broken float glass, but the pane is gone and the opening is left open.
• Laminated glass cracks, often in a spider's-web pattern, but the pieces stay stuck to the interlayer. The pane stays in the frame, still keeping out the wind and rain, and anyone trying to get through has to keep hitting it.

Where each is used

Toughened glass suits places where strength and resistance to heat matter and where a clean break is acceptable: large fixed panes that take wind load, glass close to heat, and panes that face hard knocks in daily use.

Laminated glass suits anywhere a broken pane must stay in place: glass near floors, overhead glazing, glazed doors, and any opening where security matters. The two can also be combined. Two toughened sheets laminated together give the strength of one and the hold of the other, which is common in overhead and balustrade glazing.

Which suits doors, windows and shopfronts?

• Doors. Laminated glass is usually the better choice. Doors are pushed, knocked and walked into, and a laminated pane that cracks keeps the doorway closed until it can be replaced.
• Windows. For ordinary windows away from floors and doors, clear float glass is often fine. Low windows, bathroom windows, panes beside doors and windows a child can reach are better in laminated glass.
• Shopfronts. Laminated glass is the usual choice at street level, because a broken pane stays in the frame overnight rather than leaving the premises open.

If you are unsure, the question to ask is simple: if this pane broke, would it matter that the opening was left open? If the answer is yes, laminated glass is the one to choose.

A note on security

Neither type of glass makes a home impossible to break into, but laminated glass slows an intruder down and makes a lot of noise doing it, which is often enough to make them give up. For openings that need more protection, burglar bars and security gates work alongside the glass rather than instead of it.

Get the right glass fitted

If you are replacing a broken pane or choosing glass for new doors and windows, tell us where the glass is going and we will recommend the right type when we quote. Read more about window glass replacement, or request a free quote with a photo of the window or door.