# Polka-dotted windows **URL:** \ **Category:** Factual Questions\ **Created:** [October 14, 1999, 10:35pm UTC](https://boards.straightdope.com/t/polka-dotted-windows/3936 "1999-10-14T22:35:00Z")\ **Posts on this page:** 10\ **Page:** 1
**Author:** ![Sue\_Duhnym](https://avatars.discourse-cdn.com/v4/letter/s/91b2a8/32.png) [@Sue\_Duhnym](https://boards.straightdope.com/u/Sue_Duhnym)\ **Post date:** [October 14, 1999, 10:35pm UTC](https://boards.straightdope.com/t/polka-dotted-windows/3936/1 "1999-10-14T22:35:00Z")
Lately, when the sun hits the window on a car just right, I see dots. Obviously this is some sort of window tinting, but why the dots? Most often seen on late model, expensive cars. Any ideas? ---
**Author:** ![Harmonious\_Discord](https://avatars.discourse-cdn.com/v4/letter/h/74df32/32.png) [@Harmonious\_Discord](https://boards.straightdope.com/u/Harmonious_Discord)\ **Post date:** [October 14, 1999, 10:47pm UTC](https://boards.straightdope.com/t/polka-dotted-windows/3936/2 "1999-10-14T22:47:00Z")
Did somebody use one of those rain repellant or antifog products on the window? I had to use Windex to remove the repellant from my windshield. I saw spots when the sun hit the window at an angle. ---
**Author:** ![Sue\_Duhnym](https://avatars.discourse-cdn.com/v4/letter/s/91b2a8/32.png) [@Sue\_Duhnym](https://boards.straightdope.com/u/Sue_Duhnym)\ **Post date:** [October 14, 1999, 11:00pm UTC](https://boards.straightdope.com/t/polka-dotted-windows/3936/3 "1999-10-14T23:00:00Z")
Nope… They’re very uniform dots. Almost in a checkerboard pattern…only with dots. ---
**Author:** ![rjk](https://avatars.discourse-cdn.com/v4/letter/r/ed655f/32.png) [@rjk](https://boards.straightdope.com/u/rjk)\ **Post date:** [October 14, 1999, 11:42pm UTC](https://boards.straightdope.com/t/polka-dotted-windows/3936/4 "1999-10-14T23:42:00Z")
The explanation I’ve heard is that when the windshield is made, it’s heated to bond in the plastic layer that stops big pieces from flying around in an accident, and then quickly cooled by air jets arranged in that square pattern. You see the pattern when light is (refracted? reflected?) differently according to the uneven stresses in the glass. IIRC, you’ll only see it in polarized light (like that reflected from shiny surfaces), or when you’re wearing polarized sunglasses. ## Side windows, at least, are purposely strongly treated that way so the stresses will make the glass shatter into popcorn; windshields are made with less stress because a layer of popcorn glass is _really_ bad for visibility. Bob the Random Expert “If we don’t have the answer, we’ll make one up.” ---
**Author:** ![The\_LION](https://avatars.discourse-cdn.com/v4/letter/t/8e7dd6/32.png) [@The\_LION](https://boards.straightdope.com/u/The_LION)\ **Post date:** [October 15, 1999, 12:51am UTC](https://boards.straightdope.com/t/polka-dotted-windows/3936/5 "1999-10-15T00:51:00Z")
A lot of car window tint kits use a sheet of plastic with a pattern of microscopic dots glued to the inside of the glass. Reflected light viewed thru two panes of this type of tinted glass will show a visable dot pattern. t lion ---
**Author:** ![ChiefScott](https://avatars.discourse-cdn.com/v4/letter/c/58f4c7/32.png) [@ChiefScott](https://boards.straightdope.com/u/ChiefScott)\ **Post date:** [October 15, 1999, 1:04am UTC](https://boards.straightdope.com/t/polka-dotted-windows/3936/6 "1999-10-15T01:04:00Z")
Tequila shooters and driving don’t mix. ::Pulling the spare sheets and pillow from the hall closet:: ---
**Author:** ![techchick68](https://avatars.discourse-cdn.com/v4/letter/t/ea5d25/32.png) [@techchick68](https://boards.straightdope.com/u/techchick68)\ **Post date:** [October 16, 1999, 4:37pm UTC](https://boards.straightdope.com/t/polka-dotted-windows/3936/7 "1999-10-16T16:37:00Z")
The LION, I am a former window and door sales rep and laminated glass (same as windshields) is not produced with glues. Laminated glass is actually two pieces of glass with a polyvinyl coating or sheet (plastic) in between that is bonded by heat and pressure. As to why the checkered or grid pattern happens I am not sure. Automotive manufactures have started putting some coating on the glass in recent years. In my window days, I don’t recall ever seeing windows with the grid pattern. Of course, it could be due to the reflective nature as stated previously. ---
**Author:** ![The\_LION](https://avatars.discourse-cdn.com/v4/letter/t/8e7dd6/32.png) [@The\_LION](https://boards.straightdope.com/u/The_LION)\ **Post date:** [October 16, 1999, 7:28pm UTC](https://boards.straightdope.com/t/polka-dotted-windows/3936/8 "1999-10-16T19:28:00Z")
techchick68 As an ex autoglass installer I am aware of the difference between tempered and laminated glass. What I was refering to was aftermarket window tint kits that use a plastic film with a microscopic dot pattern glued to the inside of the glass. These kits can be bought at most auto parts stores and are the type that most window tint shops use. t lion ---
**Author:** ![techchick68](https://avatars.discourse-cdn.com/v4/letter/t/ea5d25/32.png) [@techchick68](https://boards.straightdope.com/u/techchick68)\ **Post date:** [October 17, 1999, 1:06am UTC](https://boards.straightdope.com/t/polka-dotted-windows/3936/9 "1999-10-17T01:06:00Z")
Sorry LION, Spose I should read more carefully next time 🙂 ---
**Author:** ![The\_LION](https://avatars.discourse-cdn.com/v4/letter/t/8e7dd6/32.png) [@The\_LION](https://boards.straightdope.com/u/The_LION)\ **Post date:** [October 17, 1999, 1:43am UTC](https://boards.straightdope.com/t/polka-dotted-windows/3936/10 "1999-10-17T01:43:00Z")
techchick68 No problem,I am bad about skim reading myself. I use similar type films at work in the printing trade. The ones we use are available in various dot sizes. Holding two screens lined up into the light generates some very interesting patterns. t lion