All modern paint these days is usually urethanes. That being said, paint is basically plastic. The best protectant you can buy for plastic is "Plexus" . Its whats recommended for aircraft windshields, by many manufacturers. I have used Plexus on all my paintwork for years, as the final protectant ,and thats all I use on helmet faceshields. Its a bit pricey at $26. for a large spray can, but a little bit, on a micro fiber towel, goes a long way. Plexus actually "fills in" tiny micro scratches,and really improves the shine on paint. If you overspray it on other surfaces of the bike, no problem, it leaves no greasy residue. I gave a can to a buddy, who does professional custom painting/ airbrush work, and that all he has been using on his paint jobs for a few years now.