We use 1/4 inch thick UHMW (Ultra High Molecular Weight) plastic. The stuff is insanely expensive, but almost indestructible. A 0.250 inch thick 4x8 sheet is around $166, 3/8" thick is $256, and 1/2" thick is $370. We ripped it to 4" x 96" strips to use for flappers. We tried exterior vinyl molding from Home Depot, but the drywall screws eventually pull through. It doesn't happen with the UHMW plastic.
The UHMW flappers are very easy on the cars.
*** The Gate - Celebrating 7 years at the same location ***
The difference between genius and stupidity is that genius has its limits. - Albert Einstein
Understeer is when you hit the wall with the front of the car and oversteer is when you hit the wall with the rear of the car