Just thought it might be worth passing this on. Been doing a lot of night driving on rural roads recently and with the rain and traffic film on the screen and oncoming headlights it's been difficult. I've tried all sorts of methods to get the traffic film off, and even thought Rainex might help, but it made the problem worse.

At the suggestion of someone at Wilco Motor Spares, I tried detergent and amazingly it took off not only the traffic film but the Rainex too. I used one Tesco (other brands are available!) non-bio detergent tablet (like for washing clothes) crushed up with a small amount of water and spread it all over the screen with a sponge. It was left for about 5 minutes and then well rinsed off with water - result, a clearer cleaner windscreen than I've had all winter and it cost next to nothing.

I use PIAA wipers - does not hold the muck like Rain ex but still means water beads and runs off. Prep the windscreen with the wipes first then use with clean water for an initial silicon layer