Here at Coveryourcar.co.uk we used to get the odd customer calling, asking which cover was best to help stop paint stripper being sprayed onto their car. We did some testing and basically we recommended a 100% waterproof cover ( our Monsoon Car Cover ) as most if not all of the paint stripper ran off the cover. This is particularly useful in a drive by event where stripper is sprayed from a moving vehicle.
Believe me this goes on more than you would think. The cover wasnt in a particulary good state after the event but it did work. Nowadays we get about 1 call a week so this is an ever increasing problem of mindless vandalism.