I noticed these patterns in the condensation on the inner surface of my car's windshield when I turned on the defroster. Usually when I see lines like these on condensation I assume it's because of snails/slugs altering the surface chemistry of the glass, but in this case 1) the lines seem too straight to be from a snail, 2) the angles are too sharp/consistent, and 3) there aren't any snails in my car. They also don't seem to be ordered enough to be artefacts from the manufacturing process (it's a new car). Anyone have any ideas?

Condensation Pattern

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    $\begingroup$ My first thoughts were: scratches, cracks, or spider webs. The topology of the lines makes spider webs seem unlikely. Cracks in a new car's windshield would be unlikely, and the topology seems wrong. I would drag a razor blade or fingernail across one of the lines to see if I could feel a scratch. One more possibility: the windshield may have been wrapped in something that left those lines, in the form of contamination on the surface. You could try scrubbing a place on one of the lines, using acetone; then see if the mark shows up next time there's condensation inside your windshield. $\endgroup$
    – S. McGrew
    Commented Nov 5, 2018 at 14:25
  • $\begingroup$ I have never seen these patterns until recently while parking in an area that is somewhat urban. Wondered ... Could these be caused by wifi long wavelengths? This seems to be a fairly new phenomenon as I've never seen them before but read reports of it happening over the last ten years. They seem too straight and sharply angled to not be created by something that can generate somewhat of a pattern albeit random. Similar to some photos of patterns for wifi long wavelengths. $\endgroup$
    – MountainM
    Commented Dec 11, 2022 at 5:27

1 Answer 1


Condensation patterns like this are commonly caused by tiny amounts of dirt or chemical residues on the glass surface that locally alter the condensation kinetics. I do not know what caused this particular pattern but try cleaning the window off with Windex/ammonia cleaner and a clean paper towel and see if the pattern persists.

By the way, people who work in cleanrooms with silicon wafers used to exhale on a wafer to see if it was properly cleaned. If it wasn't, swirly patterns of condensation would show up indicating contamination from the previous processing step.


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