Yea plastic bumpers lol
I can't remember if it's aluminum or just chrome. Use a magnet to check. If it doesnt stick then it's aluminum.
If its aluminum then sand it down before you polish it. When I did the lips on my rims I started with 120grit and went all the way to 2000 grit. Remember to use water when you get into 400-600 grit and up. Once you are done sanding add the metal polish. Hope this helps.