There has been lots of comparison between RainX and Aquapel, because they are both made to serve the same purpose – windshield rain repellents. But they work in completely different ways, with different types of chemicals.
RainX and similar products are silicone based materials that make a filmy layer on the windshield causing the water to roll off , similar to the effect of rinsing greasy hands. But eventually it wears down and degrades. The film left behind can affect the clarity of the windshield, as well as build up on the wipers and moldings, especially if you also use the RainX wiper fluid.
Aside from leaving a white or orange crust another downside of this RainX film that develops is that it robs the moldings and wipers of their ability to retain their own moisture and stay soft. Then if the film has worn off the windshield in the wiper area and dried out the wipers, the hardened wipers themselves could cause permanent damge to the windshield.
I have found the best way to remove RainX from your windshield at home is actually with soft scrub and a paper towel which won’t damage the car or glass. Since RainX is silicone based, a grease, wax and tar remover should work and that would take off and bugs and other road grime as well. This type of product would be available at any auto parts and supply store – it’s used to remove grease and wax to prep a car for paint. Grease remover is a pretty high test chemical so you would need to wear gloves when using it and if it gets on the paint it need to be wiped up so it won’t dry there.
Aquapel, however, doesn’t leave any film on the windshield because it actually chemically bonds to the glass. It is made with a chemical engineered for the aviation industry, so the bond between Aquapel and the windshield can withstand all the ravages of time much better than RainX. Even as the Aquapel wears down some bonded particles remain, so each application lasts longer than the one before. Overall, not only does Aquapel last longer than RainX – it lasts better.