Doug- Thanks for the info. I've gotten a call from Suntuf Inc's sales guy. They do make the Palruf, which is polyvinylchloride not biaxially oriented. They also make a biaxially oriented pvc. It yields at first, then as it stretches, it becomes stronger.
Molecules go from the random state to a state where they are lined up in a plane.
Biaxially oriented pvc is, according to Matt the sales guy at Suntuf, much more resistant to impact, i.e. hail. Biaxially oriented pvc is, supposedly, also less of a problem with freezing than un-oriented pvc. For chemical resistance, PVC is actually better than polycarbonate. However, according to Matt at Suntuf, polycarbonate is still the undisputed leader over even biaxially oriented pvc for general outdoor applications. This is supposed to be a big deal.