Eli5: what are the black dots around the edge of a car window? What are they called and what do they do?
In: 40
Most of the replies here are partially right… the black band on a car window is called a frit band. It is there to protect the urethane/glue from UV radiation. The dots are there mostly for aesthetic purposes to give a nicer looking transition from the band to the clear glass. The solid bits around the mirror are to protect the glue that holds the mirror on (also sensor/camera brackets on newer cars).
Now, to dispel some myths:
1: It is not an antenna. Although there are sometimes antennas built into windows, they are usually in the back or back quarter windows and they look like defroster lines. Bonus: if you see something that looks like a defroster at the bottom of the windshield, it is… it’s a heater for you wipers that comes on with the defroster.
2: It’s not to help with adhesion. In fact, many German cars have the frit band in the laminate layer between the layers of glass. We use a urethane primer to ensure good adhesion between the urethane and the glass.
3: It has nothing to do with heat distribution. As mentioned above, it functions as a UV blocker.
Bonus fact: Your windshield is made of two layers of glass with a layer of plastic laminate between them. This means that even if there’s a crack in the glass, your windshield isn’t going to fall in on you.
Source: am a glass technician and work with automotive glass 40+ hours a week.
Disclaimer: most of these facts are generalized with exceptions but are true for most cars.
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