The use of urethane was a great improvement to the existing
plastic wheels that skaters had used previously, taken from roller skates and jury-rigged
to a board of wood.  The use of this soft
yet durable material allowed the board to grip to the ground as skaters rode
instead of slipping out from underneath them, which led to the practice of
skating empty swimming pools during a California drought (the banked sides of a
pool resemble the face of a wave).
Professional skaters started to get monetized contracts, compete in
widespread competitions, as the sport continued to spread culturally with the
introduction of the first skateboarding shoe –  released by a company called Vans in 1975.