Ethanol
The active ingredients in Rain-X work only if applied to a clean, dry surface. Lucky, then, that all of the ingredients are dissolved in ethanol. Not only is it a really good solvent, it helps remove dirt and oil from the glass, then evaporates.
Isopropanol
Rubbing alcohol. Some poor souls will try anything to get drunk, so to keep them from chugging ethanol-rich Rain-X, the company adds this stuff — it shares a few chemical properties with its cocktail-friendly cousin, but it's an unpalatable poison. Mixologize with Rain-X and you'll end up way under the weather.
Polydimethylsiloxanes (PDMS)
A chain of repeating molecular subunits — two organic methyl groups attached to inorganic silicon-oxygen — forms a thin layer on the windshield, and the methyl groups provide low surface tension, which actively repels high-surface-tension fluids like water.
Ethyl sulfate
During production, the Rain-X gods add sulfuric acid to the mix (for reasons we'll explain later). By the time it reaches your auto-parts store, some of it has mixed with ethanol and converted to this byproduct, also found in the urine of alcoholics.
Chlorotrimethylsilane
Residue from PDMS synthesis, this compound is regularly used to silanize — that is, chemically neutralize — laboratory glassware so organics won't stick. Same for your windshield, too? A Rain-X chemist told us he couldn't say for sure.
Siloxanes and silicones, di-me, hydroxy-terminated
Fragments of PDMS, broken down by that sulfuric acid we mentioned. The hydroxyl groups help them bond strongly to glass, making it tougher for your wipers to disperse the Rain-X.
