Works as advertised on any of the windows. The problems come from the wipers smearing what's left of the glycerine after the film breaks down. So, don't use it on the windscreen. It works great on any other window. It also works on the inside to reduce fogging and indeed, that was how this product got started in the 1930s. It increases the effect of surface tension in the tiny water droplets that cause fogging. This forces the tiny drops to form slightly larger drops you can see past instead of the tiny drops that cause fogging.What about the rear window, is that a no no also ?