# What's This Crud On The Inside Of My Windshield? **URL:** \ **Category:** Factual Questions\ **Created:** [March 30, 2007, 2:55am UTC](https://boards.straightdope.com/t/whats-this-crud-on-the-inside-of-my-windshield/398072 "2007-03-30T02:55:27Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![Surreal](https://avatars.discourse-cdn.com/v4/letter/s/eada6e/32.png) [@Surreal](https://boards.straightdope.com/u/Surreal)\ **Post date:** [March 30, 2007, 2:55am UTC](https://boards.straightdope.com/t/whats-this-crud-on-the-inside-of-my-windshield/398072/1 "2007-03-30T02:55:27Z")
On several occasions I’ve noticed that my windshield appeared slightly opaque, so I cleaned the exterior surface. When I noticed that the windshield was still discolored, I checked the interior surface and found that it was covered by a layer of crud, despite the fact that it had not made physical contact with anything since it was last cleaned. This residue has a waxy consistency, making the interior surfaces of the glass much more difficult to clean than the exterior surfaces. What is this substance that builds up on the interior of my automotive glass? How do I prevent it from accumulating there? Thanks. ---
**Author:** ![Sharky](https://avatars.discourse-cdn.com/v4/letter/s/bbce88/32.png) [@Sharky](https://boards.straightdope.com/u/Sharky)\ **Post date:** [March 30, 2007, 3:03am UTC](https://boards.straightdope.com/t/whats-this-crud-on-the-inside-of-my-windshield/398072/2 "2007-03-30T03:03:41Z")
I can’t find a cite to back this up, but the plastics used in the manufacture of automotive interior trim emit vapors which cause a greasy film buildup on the inside of the window glass. ---
**Author:** ![Sharky](https://avatars.discourse-cdn.com/v4/letter/s/bbce88/32.png) [@Sharky](https://boards.straightdope.com/u/Sharky)\ **Post date:** [March 30, 2007, 3:10am UTC](https://boards.straightdope.com/t/whats-this-crud-on-the-inside-of-my-windshield/398072/3 "2007-03-30T03:10:02Z")
Ah, here ya go: > [@](#): > > The nemesis of interior glass and, in fact, all interior surfaces is vinyl vapor residue: the oily vapor given off by vinyl (upholstery, vinyl dashes, other interior vinyls), especially as vinyl grows older, when exposed to sunlight. The hotter the weather-and the hotter a car’s interior-the greater the vaporization of the vinyl. Not all vinyls vaporize as readily as others; nor do all give off equal amounts of vapor. > > Most people seeing a vinyl-vapor-smudged windshield or windows assume the driver is a smoker. Maybe, but vinyl vapor leaves a far more bothersome residue on glass-and on the car’s entire interior- than any dozen packs of cigarettes. In sunbelt states, especially in summer with the windows shut, vinyl residue can come close to coating interior glass in a single day. Not only is the residue car-disfiguring, it is dangerous, limiting visibility. > > To remove vinyl residue, use any good household or automotive window cleaner, an ammonia-water solution, or all-purpose cleaner. Source: [AutoZone Pro CarCare Reference Library](http://www.procarcare.com/icarumba/resourcecenter/encyclopedia/icar_resourcecenter_encyclopedia_bodycare3.asp) ---
**Author:** ![Alan\_Smithee](https://avatars.discourse-cdn.com/v4/letter/a/2acd7d/32.png) [@Alan\_Smithee](https://boards.straightdope.com/u/Alan_Smithee)\ **Post date:** [March 30, 2007, 3:58am UTC](https://boards.straightdope.com/t/whats-this-crud-on-the-inside-of-my-windshield/398072/4 "2007-03-30T03:58:18Z")
Do you ever sneeze while driving? ---
**Author:** ![Sofaspud](https://avatars.discourse-cdn.com/v4/letter/s/8491ac/32.png) [@Sofaspud](https://boards.straightdope.com/u/Sofaspud)\ **Post date:** [March 30, 2007, 4:09am UTC](https://boards.straightdope.com/t/whats-this-crud-on-the-inside-of-my-windshield/398072/5 "2007-03-30T04:09:48Z")
[QUOTE=Surreal] On several occasions I’ve noticed that my windshield appeared slightly opaque, so I cleaned the exterior surface. When I noticed that the windshield was still discolored, I checked the interior surface and found that it was covered by a layer of crud, despite the fact that it had not made physical contact with anything since it was last cleaned. This residue has a waxy consistency, making the interior surfaces of the glass much more difficult to clean than the exterior surfaces. What is this substance that builds up on the interior of my automotive glass? How do I prevent it from accumulating there? Thanks. [/QUOTE] Are you a smoker? Smoke from cigarettes will cause a hazy buildup over time on the inside of the windshield, and it’s very hard to remove. Does this happen more often in winter, when your heater is running? I’ve had a buildup like that once when I had a pinhole leak in a coolant line; it made its way into the airstream and from there onto my windshield without noticeably affecting my coolant levels for quite some time. If no to either of these, then I’d go with the fumes from the plastics and vinyl in your car. I don’t know of any way to prevent it, honestly. Perhaps a damp paper towel over the dash when you exit? ---
**Author:** ![panache45](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/panache45/32/64_2.png) [@panache45](https://boards.straightdope.com/u/panache45)\ **Post date:** [March 30, 2007, 4:40am UTC](https://boards.straightdope.com/t/whats-this-crud-on-the-inside-of-my-windshield/398072/6 "2007-03-30T04:40:15Z")
[QUOTE=Alan Smithee] Do you ever sneeze while driving? [/QUOTE] Grrrrr, beat me to it. ---
**Author:** ![Rick](https://avatars.discourse-cdn.com/v4/letter/r/9f8e36/32.png) [@Rick](https://boards.straightdope.com/u/Rick)\ **Post date:** [March 30, 2007, 5:08am UTC](https://boards.straightdope.com/t/whats-this-crud-on-the-inside-of-my-windshield/398072/7 "2007-03-30T05:08:00Z")
It is the outgassing of the various materials used in the interior of the car. If you use Armor-All or some such stuff, it will be worse. Some cars use interior materials that are more or less hypoallergenic and these fog the windshield much less than cars that aren’t. For example the interiors used in Volvos meet the [Okotex 100 standard](http://www.e4s.org.uk/textilesonline/content/6library/report6/8_eco_labelling.htm) Not all cars meet this standard. Older cars were much worse. Early 70’s cars from Japan would fog the inside of the windows is a week or two. You best bet to keep your windows sparkling clear is to clean them often either go to a full service car wash, or do them yourself every week or two.