Quoted from pinaholic:What is PWR?
I think he meant "PRW" which is Marco Specialties "house" rubber brand. From what I've read, it's based off of the "ABC" rubber that William's and Bally used to use years ago (which was very high quality).
From what I've read, it's pretty much the highest quality rubber available today. I tend to agree with those sentiments. It's much better quality than rubber I get anywhere else.