Why is the inside of my windshield greasy

Why Is The Inside Of My Windshield Greasy?

It happens to us all. You’re driving along, and suddenly your windshield develops a greasy film. You , “Oh no! Did I just run over something on the road?” but then you realize what’s really going on: the inside of you thinks glass is coated with a layer of grease that’s caused by a chemical reaction between two types of silicone. It’s not always easy to understand why things like this happen (especially if you’ve never taken chemistry), but we’ll walk through how it works so that next time it happens to you or someone else (it will), they won’t be completely baffled by this phenomenon.

Windshields are greasy because of a chemical reaction.

If you have ever noticed that your windshield has a greasy film on it, it’s probably because of the silicone used in the production of glass. A layer of polyvinyl siloxane is bonded onto the glass, which acts as a lubricant during production and also helps prevent cracking and breaking while driving through the elements. This bonding is what keeps your windshield clean over time; without this protective layer, dirt would stick to your window more easily and leave streaks that would be difficult to remove.

Why does it work?

The silicone is a lubricant, which helps to ensure that your windshield wipers glide easily across the glass. It also serves as a sealant, keeping out moisture and UV rays which can damage the windshield over time.

It's just physics!

The inside of the windshield is greasy because it’s just physics!

It’s all about the molecules. The glass in your windshield is a liquid, so when you drive in cold weather and the air outside is much colder than you are, water condenses on your windshield and forms ice crystals. When those ice crystals melt, they leave behind a layer of silicone where they used to be. This silicone layer looks like grease but isn’t actually dirty—it’s just slightly more slippery than plain old glass.

The secret is silicone.

Silicone is a type of oil that has a lower surface tension than water, meaning it spreads out more easily. When you spray this onto your windshield, you’ll notice that it leaves an oily film on the glass—this is the silicone grease we are talking about!


The reason why windshields are so greasy is because of a chemical reaction between the glass and the silicone in the wiper fluid. The silicone helps protect both surfaces, while also giving them a tacky feel that makes them easier to clean. You might also notice that your windows feel slippery when they’re wet, which happens because these materials have low surface energies and can repel water from their surfaces.

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