My experience is as follows. I have an A4 Cabrio (canvas). Water would enter within the first ten minutes of light rain. Last year, I applied a liter of FabSil (almost two coats), and nothing came in until this year. Even before the heavy rains started, it always repelled light rains. However, I messed up and didn't reapply this year before the rains started. Anyway, I reapplied it this year, but I didn't do a good job, and I ended up with 1.5 coats. Still, I would say I have about 95% coverage (if not better). It needs to rain very heavily, and even then, it only drips slightly in the passenger seat and a little on the rear pillars. I will get this to apply a second coat; I believe it will fix it. In the first year, not a drop came in anywhere.

Purchased to be used on a car soft top, for waterproofing. After 10 rains in less than three months, it seemed that it no longer repelled water like it did during the first rains (I would expect it to last longer before needing to reapply). Fortunately, I accidentally found another chemical and was saved.