A.P.K has it right - heavy high-load particle cover but it's called "retroactive" due to the urethane base. However be VERY careful about polishing it. My dad had one, polished it, and nobody (proshop included), could get back the original reaction when he wanted to change it back. Didn't matter what was done to it, how it was sanded, etc., it never rolled the same way again - he had to buy another. So be warned, there is a good chance if you polish it for longer, less hooking reaction, you won't be able to recover the "box" type reaction.