Cheap or Ceramic Window Tint? The Difference in Summer

The car stands for an hour in a summer car park. When you get back in, you cannot hold the steering wheel or sit down on the seat. You decide to have the windows tinted, you collect two quotes — and both give the same figure: 35 percent light transmission. Yet the prices differ several times over.

That figure says one thing only: how much light passes through the glass into the car, that is, how dark the window will be. About that hour in the sun, and about the hot steering wheel in it, it says nothing.

Why a parked car gets so hot

At midday, with thirty-five degrees outside, the temperature in an uncovered cabin climbs to 65 to 70 degrees. Brightness is not the cause.

What heats the car is not the light you can see in the window but infrared radiation — your eye never catches it, and it is exactly what settles into the steering wheel and the seat over that hour in the car park. Darker glass takes away brightness. With the part that heats, it does nothing on its own.

How dark the window is and how warm your cabin gets are therefore two different things. The second one is the work of the layer inside the film — and that is precisely where your two quotes differ, even though both state the same percentage.

Dyed film: the window went dark, the steering wheel still burns

Dyed film is the oldest type used on windows, and it tends to be the cheaper quote. Its dark tone comes from a dye dissolved directly in the layer.

The dye holds back light, so the window really does go dark. Infrared radiation, however, passes through almost unchanged, and the cabin warms up just as it would without any film — there is simply less light inside. After that hour in the car park you reach for a steering wheel that is just as hot, only behind darker glass.

The dye also changes in the sun over time, and the window takes on the purple-brown cast you see on older cars. At that point nothing can be done but take the film off and fit a new one.

Metallic film: cooler, but the phone loses signal

The second route to a cooler cabin runs through metal. Metallic film has a thin vapour-deposited layer of metal that reflects visible light — hence the mirror-like look — and with it a large share of the infrared and nearly all of the ultraviolet. Unlike dyed film, it genuinely does address heat.

But that same metal layer behaves like a Faraday cage and screens radio waves as well. You notice on the first day: the GPS on the dashboard hunts for a signal and the phone in the car is a bar or two down.

We therefore do not install metallic film, not even on cars without navigation. You would pay for the cooler cabin by having the car stop doing things you are used to.

Nano-ceramic film: the same dark window, fifteen degrees less

The third route relies on neither dye nor metal. Here the heat is caught by ceramic nanoparticles ten to fifty nanometres across, dispersed through the layer of the film.

Those particles reflect infrared radiation back out, while visible light passes through them. And because they are smaller than its wavelength, they do not scatter it either — the film does not look milky or mirror-like, and the window goes only as dark as the shade you pick. How dark it ends up is therefore your choice, independent of how much heat the film holds back.

So the window can have the same 35 percent light transmission as the cheaper quote and the cabin temperature still drops from those 65 to 70 degrees to 50 to 55. Fifteen degrees is the difference between a steering wheel you cannot hold and one you can. Meanwhile ultraviolet radiation practically never reaches your hand or your face.

There is no dye in such a film, so there is nothing to fade and the window will not turn purple the way a dyed one does. And unlike a metal layer, it does not stand in the way of radio waves — the GPS and the phone in the car keep working.

The demo above shows what makes the three films different inside — dye in the layer, vapour-deposited metal, or ceramic nanoparticles — and why two equally dark windows behave differently in the sun.

What to look for in a quote you get elsewhere

Nano-ceramic films are described in quotes as radio-transparent and state how much radiation they catch: a good film 94 to 98 percent in the band around 1025 nanometres, where the sun gives off the most heat, and over 99 percent of the ultraviolet. The ceramic oxides in the layer are usually named — antimony tin oxide, indium tin oxide, or composites based on SiO₂.

These tell you whether the other quote is talking about heat or only about darker glass. One of those figures shows up on the road as well: air conditioning in a tinted car uses roughly 60 to 75 percent of what it would use in the same car without film.

What we will ask you before we start

Newer cars have a camera in the windscreen for driver-assistance systems; in the manual you will find it under the abbreviation ADAS. If you're also having a sun strip fitted on the windscreen, we take this camera into account: it looks out in near-infrared, in the band around 850 to 940 nanometres — precisely the one the film is meant to hold back.

Film for such a car therefore has to be certified for that specific camera system, otherwise the camera may not see correctly after installation. So we ask about your car's equipment before we start work on it.

Write to us about your car

We install nano-ceramic films only, SolarScreen and KEETEC. We do not offer dyed or metallic ones — so the price you compare is only between films that actually do something about the heat in the cabin, on the window tinting page.

Write to us about the car you have and how dark you would like the windows. We will look at it and recommend the option that leaves you able to hold the steering wheel after an hour in the car park.

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