I'm not sure if the different parts of the car are layered differently. Best protection against rockchips is clear-bra. It's pricey, but long-term it's worth it IMO. Of course you have to bring the paint up to par before you do it.
I bought my 2006 330i last summer. It already had a bunch of rock chips on the bumper, and when I started driving it, it started getting chips on the hood too
I touched up the chips on the hood and deep scratches all around the body with Dr. Color chip. I had a body shop paint and blend the lower portion of the front bumper. Then I had a color-correction detail, opti-coat, and clear-bra done. Hopefully I'll be set for however long I own the car
looks awesome now
I *think* on our cars the paint is:
//clear-coat
\\base color
//primer
\\metal/plastic
on all body panels (maybe plastic bumpers don't have primer? or have extra adhesion layer?) someone correct this please