Drivers are just realising what dots on inside of car windows mean

Anyone who has taken a driving test will be aware of how much there is to learn about your car – but it appears there is one common feature of your vehicle that many drivers are only just learning about.

Having spotted a series of black dots surrounding his windscreen, Rory Thomas took to Reddit to seek advice on their purpose. Sharing a snap from within his car, he asked: “Why do vehicle windscreen have these dots?

He continued: “I can see how in some cases it will lower the harsh sunlight, but this window seems to just have them around the edge.” His post was met with a response from hundreds more Reddit users, some of whom were equally as perplexed, whilst others attempted to offer an explanation.

One person admitted: “Crazy! I was just on a bus yesterday and thought about this.” Whilst a second quipped: “Dunno but these legit saved me when I went to court over a parking ticket and had the case dismissed. Praise the dotted windscreen edge!”

Several Reddit users, meanwhile, explained that the dots are known as “frits”, and are pieces of black-painted enamel that are baked into the borders of the glass during the manufacturing process. But what purpose do they serve?

“You need a black band around the edge of the windscreen to shield the glue/seal from the sun drying it out and killing it with UV,” one Reddit user explained. “If you just placed the black band it would get hot and you’d have a temperature difference between the see through glass and the black layer. The dots are a dithering pattern to make the temperature change more gradual.”

Whilst someone with inside knowledge of the industry elaborated: “I work in the glass automotive manufacturing business. It’s called a dot matrix. The band itself is mandatory to cover up glue and the trim,the dot matrix is purely aesthetic.

They continued: “The same window will have different band types depending on which market the glass is sold in. For example, the Nissan Frontier back window has 10 different varieties, all made in the same place… same basic piece of glass, 10 different designs based on markets. We just change a silk screen and use the same raw pattern glass.”

And a third person concurred: “As mentioned above it is called frit, the reason for it being black is to prevent sun light to pass through and reach windshield adhesive which is urethane based and tends to become more solid instead of viscoelastic and breaking apart easily, that is important because when cars crash a big ammount of energy goes to the windshield and can fly away killing people.

“Also as side note when you install windshields there’s a kind of black paint application directly to frit that helps blocking light and etching the glassy surface of the frit for a better adhesion.”

Indeed, vehicle glazing and tiniting specialists, Autoglaze confirms online: “These dots are actually called frits. A frit is a painted black enamel that’s baked around the borders of a windscreen during the manufacturing process. They often start out as solid black bands near the edge, and gradually dissolve into small dots at the outer edge.

“They are seen on windscreens and other parts of your car’s glass windows. And believe it or not, they actually serve four main purposes:

1. They serve as a contact point between the glass and car frame. They create “etches” on the surface, making them rougher so the adhesive can stick better to the glass.
2. They help preserve the urethane sealant used to bond the glass to the frame. They use the black enamel outside the windshield to block the sun’s ultraviolet rays from melting the adhesive underneath the band. This keeps the windows firmly glued in their place.
3. The black dots, or “dot matrix” actually help distribute temperature evenly to lessen optical distortion or “lensing”. This happens when the frit band (the solid black one) heats up much faster than the windscreen’s glass, creating an optical distortion that makes either straight lines look curved or bowed inwards toward the centre. Those “gradually sinking” black dots help lessen this phenomenon by dissipating the heat and spreading it out evenly.
4. Frits are also there for aesthetic purposes. If you look closely, the contrast between the dark band and the transparent glass can look too obvious even when viewed from afar. Creating a halftone pattern or “dot-matrix” allows a gradual decrease in size, making the transition much more subtle and easier on the eyes.”

So now you know!