About Skate Park Formula(TM) (SPF) Skatepark Formula(TM) (SPF) is very high quality urethane specifically formulated to resist flatspotting on slick or smooth surfaces while maintaining a higher rebound for a quicker response and a faster roll. Skatepark Formula(TM) has a high resistance to abrasion while not compromising hardness and slide ability. Simply puta | Skatepark Formula wheels grip better on slick surfaces, are almost impossible to flatspot, and are the fastest, longest lasting wheel on the market today. You won&&';;t find our Skatepark Formula from any other wheel supplier so get a set and find out for yourself what the word on SPF is all about.