Types of glass explained

Toughened, laminated, low iron, annealed, toughened-laminated, smoked. The terms can blur together. Here is a simple guide to the main types of glass we work with and where each one belongs.

Nearly all of it starts as the same material. Float glass is made by floating molten glass on a bed of molten tin, which is what gives it perfectly flat faces. What happens next, heat treatment, bonding, coating, is what turns it into the various products below.

Annealed (float) glass

Standard window glass. The cheapest type. Breaks into long shards on impact, which is why it is rarely used in bathrooms, balustrades, or anywhere a person could fall against it. Used for picture frames, internal cabinet glass, and standard non-safety windows.

Annealed is the only type on this list that can be cut, drilled and edge-worked after manufacture. Everything toughened has to be finished to final size first. That single fact drives a lot of what follows.

Toughened glass

Annealed glass that has been heat-treated to make it roughly five times stronger. Crucially, when it does break, it shatters into small blunt pieces rather than long shards. This is what we use in balustrades, splashbacks, shower screens, glass doors and any application where safety is the priority. Specification: BS EN 12150.

Two things worth knowing. First, it cannot be modified after toughening. Every cutout, hole and polished edge is done before the panel goes through the furnace, so a socket in the wrong place means a new panel, not an adjustment. Second, toughened glass can very occasionally break spontaneously, years later and with no impact, because of microscopic nickel sulphide inclusions in the original float. It is rare, but it is the reason toughened alone is not acceptable where glass is the only thing preventing a fall. See our balustrade regulations guide.

Laminated glass

Two or more sheets of glass bonded together with a plastic interlayer (usually PVB). When it breaks, it stays in place, held together by the interlayer. Used in overhead glazing, walk-on floors, and anywhere where falling glass would be unacceptable. Often combined with toughening (toughened-laminated) for the strongest possible safety result.

The interlayer brings two useful side effects. It blocks the large majority of UV, which is why laminated is worth considering where furnishings or artwork sit in direct sun. And it damps sound noticeably better than a single sheet of the same total thickness, which is why acoustic laminated glass exists as a product in its own right.

Toughened-laminated

The "best of both" option. Two sheets of toughened glass bonded with a PVB interlayer. Used for structural balustrades, walk-on glass, glass canopies, glass floors and external balconies. Strong, safe, and stays in place when broken.

Where the structural demand is higher, the PVB interlayer can be replaced with a stiffer ionoplast such as SentryGlas, which holds a broken panel far more rigidly. It costs more and it is specified rather than chosen: on a frameless balcony or a walk-on floor it earns its money.

Low iron glass

Standard glass has a slight green tint because of iron content. Low iron has had the iron removed, giving a true clear or true colour. Recommended for white splashbacks, pale shower screens, and any application where colour accuracy matters. Costs about 15% more than standard.

The easiest way to see it: look at the edge of an ordinary pane. That deep green line is the iron, and you are looking through the full thickness. Over a dark colour it is invisible. Over white or a pastel it shifts the colour perceptibly, and it is the most common cause of disappointment with a pale splashback. Low iron also matters in mirrors where accurate reflection is the point.

Tinted and smoked glass

Glass with a colour added during manufacture. Smoke (grey), bronze and dark grey are the most common tints. Used for shower screens, partitions and feature glass where a contemporary look is wanted.

The tint is through the body of the glass rather than a surface film, so it cannot scratch off, and the effect deepens with thickness. A 10mm smoked panel reads considerably darker than a 6mm one in the same tint.

Patterned, frosted and obscure glass

Glass with a texture or pattern that obscures the view through it. Used for bathroom windows, partition manifestation and decorative glass.

Obscure glass is graded 1 to 5 for privacy, 5 being the most obscure. A bathroom window generally wants 4 or 5; an internal door where you want light but some separation might want 2 or 3. Acid-etched or satin glass gives a uniform frosted face rather than a pattern, and it is the more contemporary choice, though it shows fingerprints more readily than textured glass does.

Mirror glass

Glass with a silvered or aluminised back. Standard mirror is silver-backed; low iron mirror gives true colour reproduction; antique mirror has been hand-distressed for a worn look.

For bathrooms, ask for a mirror with a moisture-resistant backing. Standard mirror in a wet room will eventually black-spot around the edges as moisture creeps under the silvering. Gym and studio mirrors are usually specified as safety-backed, with a film bonded to the rear so that a broken panel holds together. Our bespoke mirror service covers all of these.

Choosing in practice

Three questions settle most specifications.

Could someone fall against it, walk into it, or fall through it? If so it must be safety glass: toughened, laminated, or both. This covers balustrades, shower screens, glass doors, low-level glazing and anything in a critical location under BS 6262-4.

Is it overhead or walked on? Then laminated, or toughened-laminated. Toughened alone is not acceptable above head height, because if it fails the whole panel comes down as granules.

Does the colour need to be true? Whites, pale colours and accurate mirrors want low iron. Dark colours do not, and paying for it there is money wasted.

If you are unsure, that is what the free survey is for. We would rather specify it correctly at the start than replace it later.