This article is from the Watercooled VWs General FAQ, by Jan Vandenbrande with numerous contributions by others.
A: Generally you are looking for a cover which is soft where it contacts
the car paint, resists water from penetrating, breathes (trapped
moisture dulls paint), and is mold resistant.
Car covers made out of "Evolution 3" made by Kimberly Clark, or Technalon
material seem to be the current favorites and satisfy the above. They do
get wet with heavy rain or when the water repellent stuff wears off after a
couple of washes.
(For a sample call in the US (800) 424 80 00, code= 44-12-36).
They are also pretty bulky, and if wet, heavy.
I hose my covers down every couple of months and occasionally wash them in
an industrial washer. Apply Scotch Guard to make it somewhat water
repellent again.
Nylon covers are next to worthless.
To minimize paint scratches, keep your car clean, keep the cover clean, and
"roll" rather than slide the cover on.
I have also found that rolling it on and of is by far the easiest way to
cover the car. Install from the front.
Get a lock, and the cover then serves as reasonable theft deterrent as
well.
 
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