How do you clean the inside of your car windshield?

Had a friend tell me a secret about getting that grey film off.I tried it and it works.1st clean the inside of your windshield with a good window cleaner.I prefer Invisible Gl.After it's clean use Rain X on the inside of the windshield.That grey film will still get on the windshield but it doesn't stick to it.Keep a clean,soft towel in your trunk.When you notice the film starting to get on the windshield you can wipe it off with the towel.When you want to give the windshield a good cleaning,use a water dampened cloth or sponge and towel dry.It comes out clean and streak free.