The 17" Monzas are a conventional cast aluminium alloy wheel, and merely painted in a bog standard silver metalic paint.
The 18" Monza IIs look visually similar, however, they are constructed very differently. I
think they are forged (much stronger than casting), and also have Silicon and Magnesium mixed in the alloy. They also have a "hollow rim" construction, to reduce gyroscopic forces. The obvious visible difference is the anthracite grey paint on the inner surfaces, the diamond cut outer face, and the clear laquer coating.

Oh, and neither rim is made by VW, they are both made
for VW,
by BBS.