Caravanshaka,
I dont think it is the film manufacturer who is at fault. I have been into auto detailing for awhile now. I think it might have to do with your Zaino.
There are two issues at play here.
1) There have been many documented cases where Zaino users have experienced yellowing when using it on paint protection film. These have come from users of different brands (3M, Avery, Venture, etc.), indicating that it has nothing to do with the film, but more an interaction between the Zaino and the polyurethane. Zaino is a fantastic product for paint, but thermoplastic polyurethane is not paint. Would you use Zaino on your carpet? Of course not, because it is not made for carpet, right? Use something on the film that is made for paint protection film and you will no doubt have better results.
2) Yellowing is also caused by embedded contaminates (usually hydrocarbons such as oils from the road, diesel smoke and other pollutants). If you want to keep the film clean, there are cleaners designed specifically for PPF on the market for that. Use the cleaner when you wash your car just as you would use bleach when you wash your whites in the laundry. This will prevent the contaminates from building up in the pores of the film, which will prevent discoloration.
E
