Oct 28, 2023

A good view and protection. What’s important in car glass?

Windows and glass are an indispensable part of modern cars, and few people give them much thought. But they have a number of functions and the technology involved can be fascinating. Take a look.

Windscreens, rear windows, side windows and even panoramic sunroofs – the various pieces of glass and windows are standard parts of cars that don’t undergo revolutionary changes. So you might think that car windows are all the same and don’t really evolve. Although the manufacturing technology and legislative and functional requirements have remained essentially unchanged for decades, the realm of glass and windows does evolve and explore new horizons.

Panoramic sunroof on the Škoda Kodiaq

There are basically two basic types of glass used in cars today. “There is single-layer tempered glass and laminated glass,” explains Milan Sluka, who deals with glass and windows at Škoda Technical Development. Single-layer tempered glass is used mainly for side windows, but also, for example, for the opening parts of sunroofs. “Tempered glass breaks into small shards that are much less of a safety risk to the occupants than large, sharp glass fragments,” explains Sluka, explaining the reason this kind of glass is used.

Laminated glass is essentially made up of three parts: two layers of glass with a thin film between them. “This kind of glass does not shatter when it breaks, so it is used without exception in windscreens, where there are strict requirements to prevent objects from penetrating the glass,” says Sluka. Laminated glass can also be used on side and rear windows, typically to help to improve soundproofing.

Milan SlukaŠkoda Technical Development

Tempered side windows are typically shaped on a roller track, where a flat section of glass is bent into the desired shape. For windows with a two-plane curve, gravitational deflection of the heated pane of glass is used as the basic manufacturing method, but for more complex shapes the shape still needs to be pressed in a mould. Windscreens of very complex shapes can be produced today, but the more complex it is, the higher the price. At the same time, the more curved the glass is, the more it will distort the view. These parameters are carefully controlled by Škoda, and in terms of the quality of the view the Czech carmaker follows strict Volkswagen Group standards that are even stricter than the legislation.

The legislation is mainly concerned with car windows’ transparency. The windscreen and side windows in the front must have a minimum of 70% transparency, otherwise the car cannot be driven on the roads. “That’s why various third-party films that darken the windows are problematic,” explains Sluka. Simply put, the front windows cannot be tinted. A certain level of opacity (up to 30%) is provided by the glass material itself and maybe the presence of windscreen heating technology.

The windscreen heating with a thin tungsten wires has a very subtle structure that in no way impairs the view.

“The film between the two layers of glass can contain thin tungsten wires, while a more modern solution is a thin metal layer applied essentially by steaming,” says Sluka. Škoda uses both solutions, with Fabia, Scala and Kamiq customers able to order heated windscreens with thin wires, while other models (from the Octavia upwards) feature a metal layer solution. “For many drivers, this is easier on the eyes. Even if the wires are not normally perceived by the driver, they can be distracting for some,” Sluka points out.

The Škoda Scala, here in the Monte Carlo version, has distinctively shaped glazing in the boot door, with the glass extending to below the brand logo.

The windscreen must provide a good view not only for the driver, but also for any cameras and other sensors the car has fitted under the windscreen. At the same time, the windscreen is now an important “projection” surface for modern head-up displays. In these windows, there is a special film that compensates for image doubling, also known as ghosting. Also important is the shape of the window, which should not contribute to the distortion of the image.

While good vision is a priority at the front, at the back designers come up with various functional compromises for the glass. “With tinting, it’s all about making the cars’ occupants feel comfortable in the car. Too dark a window could create too dark an atmosphere inside the car,” says Sluka, adding that this is what Škoda’s designers had to think about with the Sunset package, which features tinted windows. Again, tinting can be achieved in two ways: either by adding a coloured pigment directly to the molten glass, or by using a coloured film that forms the inner layer of the laminated glass.

In modern cars the windscreen doesn’t have to ensure a good view just for the driver, but also for various assistance system sensors and cameras.

One area that is not so bound by strict regulations on views is sunroofs. These have to meet safety requirements, of course, but transparency, for example, is not covered by the legislation. It’s logical that a panoramic roof window should make the interior feel airy, but at the same time it has to protect the interior as much as possible from excessive heating. Roller blinds are only a partial solution in this respect, which is why many cars no longer use them.

Letting in enough light and brightness – that’s one of the goals for the sunroof.

The Škoda Enyaq, for example, has introduced a modern panoramic sunroof that provides thermal protection for the interior by means of a thin metal layer inside its laminated structure. This layer reflects the sun’s rays and protects the interior better from overheating. In addition, a special anti-reflective layer is applied to the inside of this window. Milan Sluka offers the explanation: “The darker the glass, the more sensitive the human eye is to various reflections.”

Truly modern and plenteous glazing can be found in the Enyaq family of cars.

It is with panoramic sunroofs that manufacturers are coming up with various other innovations. The latest developments are windows that can be darkened or lightened according to the current situation and the occupants’ wishes. “We will certainly see windows like this on Škoda cars in the near future,” Sluka promises.

Glass first appeared in cars at the beginning of the 20th century, and period photographs show that some Laurin & Klement models dating from before 1910 featured a classic flat windscreen like a window pan. After that year glass became more common, and from about the 1920s onwards, windscreens were taken for granted, with additional glazing added for side and rear windows on some body styles. While in the early days of motoring the glass was really simple, there has been considerable evolution since then. Laminated safety glass appeared in the 1930s and rounded glass arrived in about the 1950s. These innovations caught on very quickly: while the Škoda 1200 produced from 1952 had a windscreen made of two flat panes, the Škoda 440 Spartak, introduced in 1955, already had a rounded windscreen and rear window. Much of automotive glass technology was therefore developed many decades ago. This also applies to the functions that glass must still fulfil today: it must guarantee the driver a good view, it’s an important safety feature, and it also helps to achieve the best possible thermal comfort.

Despite these developments, car windows are basically timeless parts that last “forever”. “If the glass doesn’t break, the lifespan is basically unlimited,” explains Sluka, adding that car glass doesn’t require special maintenance. “It’s just a good idea to check the wipers and occasionally clean or replace them so that fine dust particles and small stones don’t scratch the glass,” he adds. That kind of damage is virtually unrepairable on a car window and could be flagged up as a problem during the car’s regular inspections.

The fact that car glass is almost entirely recyclable is crucial to the environmental considerations that are so prioritised today. “Only car glass can’t be reused to make more car glass because of the impurities in the recyclate,” explains Sluka.

An interesting detail about the car’s front and rear windows is the way they are fitted to the bodywork. Whereas in the past the glass was fitted over a rubber gasket, today the glass is glued with special flexible adhesives. These ensure that the glass and body can work together during various kinds of thermal expansion, but at the same time the glass remains an important part of the overall car frame. The first bonded glass appeared in the first Škoda Octavia, while the last model that still used sealing to help fit the glass was the Škoda Felicia.

Milan Sluka