Laminated safety glass (PVB) explained

Laminated safety glass is one of the most useful kinds of glass in a home or business. This guide explains how it works, what the PVB interlayer does, the general performance classes you will come across, and what laminated glass does for safety, security, sound and sun damage.

What laminated glass is

Laminated glass is made of two or more sheets of glass bonded to a tough, clear plastic interlayer. The most common interlayer is PVB, short for polyvinyl butyral. The glass and the interlayer are assembled, pressed together and heated under pressure, so the PVB bonds firmly to the glass and becomes completely clear.

A common example is 6.38mm laminated glass: two 3mm sheets of glass with a 0.38mm layer of PVB between them. It looks much like ordinary glass and fits most frames that take ordinary glass, which makes it a practical upgrade when a pane is replaced.

What the PVB interlayer does

The glass on either side of the interlayer breaks as easily as any other glass. The PVB is what changes the outcome. When the pane is hit hard enough to break, the glass cracks but the fragments stay stuck to the interlayer. The pane usually stays in the frame in one piece, cracked but whole, until it can be replaced.

That single property is where nearly all of the benefits of laminated glass come from.

Performance classes

Laminated glass is made in different builds for different jobs, and you will often see them described in three general classes.

• Normal strength. One interlayer between two sheets. This is the everyday safety glass for windows and doors in homes.
• High performance. Thicker glass, a thicker interlayer or both, for larger panes, glass at greater risk of impact, and shopfronts.
• High impact. Several sheets and several interlayers built up together. The more interlayers there are, the more blows it takes to get through, so this kind of build is used where resisting a determined attack matters.

The right class depends on the size of the pane, where it is and what it needs to resist.

Safety

The main reason laminated glass is used near floors, in doors and in low windows is that it holds together when it breaks. There are no large falling shards, and a person who falls against the pane is much less likely to go through it.

In South Africa, safety glazing in buildings is tested to the SANS 1263 standard. In general terms, the standard sets out how safety glass must behave when it breaks and where in a building safety glass is needed, such as glazed doors, low panes and glass close to the floor.

Security

An ordinary window breaks with one blow. Laminated glass has to be hit again and again to make a hole big enough to reach through, and each blow is loud. For an intruder, that turns a quick smash-and-grab into slow, noisy work in plain view, which is often enough to make them give up. For openings that need more protection still, laminated glass works well alongside burglar bars and security gates.

Sound

Because the interlayer is softer than glass, it damps vibration, so laminated glass generally reduces noise a little better than a single sheet of float glass of similar thickness. Interlayers made specifically for sound insulation also exist. If traffic noise is your main concern, remember that the frame, the seals and how the window is fitted matter as much as the glass.

UV and fading

PVB blocks most of the sun's ultraviolet light, the part that fades furniture, flooring, curtains and pictures. Laminated glass does not turn a room into a shaded one, since visible light and some heat still come through, but it slows fading noticeably compared with ordinary float glass.

Where laminated glass makes sense

• Glazed doors, sliding doors and folding doors
• Low windows and panes close to the floor
• Bathroom windows and windows a child can reach
• Ground-floor windows and glass that faces the street
• Shopfronts and office entrances
• Overhead glazing, where broken glass must not fall

For how laminated glass compares with toughened glass, and when each is the better choice, see our guide to laminated vs toughened safety glass.

Replacing a pane with laminated glass

Most frames that take float glass can take laminated glass instead, so the upgrade usually happens when a broken or cracked pane is replaced. Our window glass replacement page explains how a pane is replaced in aluminium, wooden and steel frames. To have laminated glass fitted, request a free quote with the size of the pane and a photo of the window.