Rain-x and other hydrophobic coating are great products. The most widely used and marketed is the Rain-x and Rain-x is the one most problematic to the windshield repair industry.
Rain-x bleeds into the breaks and cracks from wiper use. It chemically bonds to the glass and then blocks windshield repair chemicals from bonding to the windshield. This costs the windshield repair technician the price of the repair job but it also costs the consumer hundreds of dollars for a new windshield.
Rain-x is now in windshield washer fluids and car washes are using it on the entire vehicle. See Modern Car Care. Now it will be directly injected and deposited by capillary action into breaks and cracks and the car owner will not even be aware of it.
This problem was brought up to the National Glass Association, National Windshield Repair Committee by Richard Campfield. This committee and another NGA committee worked to find a solution to the problem but the consensus was that there was none. The solvents that can break the Rain-x link either leave behind a contaminated residue or are so harsh they damage the PVB.
We contacted Rain-x and asked how to remove Rain-x and they recommended Soft Scrub, but we cannot scrub the interior of a crack or stone-break. It has to be a solvent that can break the Rain-x link; evaporate and not leave behind a residue that is a contaminant to windshield repair resin. Ultra Bond is at work on this chemistry and will have a solution to this problem shortly.