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On our 2021 motorhome, the windshield developed a hairline crack (no rock chip, cannot be felt both front and rear of the glass. Just visible line). The same goes for our 2022 Jeep Rubicon. Someone from the RV forum mentioned "stress crack". Not sure of what cause that though.

Nope. Windshields are laminated glass - side windows and sunroofs are tempered glass.

Tempered glass has a very thin "tempered" layer on one side only. It is hard to break with a blunt object, yet it is easily pierced with a sharp point which will cause the glass to "explode" with the release of the temper layer. The "sharp point" can also be a small pressure point of constriction against the temper layer when a flex is applied to the piece of glass.

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