Convertible Rear Window Cover

BMW didn't start putting glass windows on the rear of a convertible until the E46 in 2000.
So, if you have a BMW convertible 1999 or older you have a plastic rear window.

The plastic scratches during normal use. Convertible tops wear during normal use.
Having a cover over the window when putting the top down helps reduce wear.

You can buy a cover or make one yourself like I did.