Why Do Cars Have Black Dots on Their Windows?

In some cars they are almost imperceptible. In others, they cover several centimeters of the windows and windshield. Either way, you've likely encountered this curious perimeter of black dots or black bands on the rear glass. Why are they there? What's the idea? At first glance it might seem like a manufacturer's whim, but in reality they have good reasons…

The Role of the Frit

The English term for this pattern of dots is "frit", and its first role is to protect the adhesive that holds the windshield in place. Ultraviolet radiation doesn't rest, and over time it could deteriorate the adhesive, compromising its integrity. The dot pattern prevents that, but there's more:

Aesthetic and Practical Reasons

The second parameter is aesthetic. Windshield adhesives have improved greatly, but when installing a new glass or replacing a damaged one, installers must work on the area, removing the old glue and using adhesion promoters. Many factors could affect the final appearance of the perimeter, so the black band and dots serve to mask those possible defects.

The dot pattern goes from larger to smaller in order to go unnoticed (not always succeeding) and minimize driver distractions. At the same time, they are a form of temperature control. When the glass receives its definitive shape and curvature, the black area of the perimeter heats up faster than the rest. The dots offer a kind of diffusion, reducing any optical distortion. The dots at the top of the windshield help protect the driver's eyes. Nothing prevents us from lowering the visor, but its coverage is never perfect, and the dots try to compensate for that detail.

Certification Marks

It's also possible to find other elements on the windshield. For example, the term "AS" indicates the glass certification. "AS1" is only for windshields, and reports a minimum clarity of 75 percent, while "AS2" and "AS3" are valid only for the rest of the car (minimum 70 percent clarity). Are you seeing a letter "E"? In European Union cars, that value tells the country of certification (if memory serves me right, Spain is E9).

Defrosting Lines

Finally, what about the lines on the rear glass? They are part of the defrosting system in some vehicles. Small currents pass through the lines, increasing the glass temperature enough to keep ice or condensation at bay.