Polyurethane Surfboard Foam has been the industry standard ever since Hobie Alter of Hobie Surfboards and Gordon Clark of Clark Foam began experimenting with it in Southern California, as a replacement to the heavier and harder to work with Balsa Wood Surfboards. Since the closure of Clark Foam in 2005, other materials are starting to make head way, most notably, EPS Surfboard Foam.
However, PU Surfboards still hold as the industry standard as it has unmatched flex characteristics and is so versatile in it's application and the resins that can be used with it. Compatible with either Polyester Resin or Epoxy resin, PU Foam is still the most versatile. But, look for shapers blending these materials like DHD's Epoxicore construction which combines both PU and EPS foam for a board with unique flex patterns where you want them.
Knowing whether PU or Epoxy is best for your surfboard and some of the ways shapers Craft Your Surfboard using different Construction Types can help you make better informed decisions on your next surfboard order.