For years,
polyurethane surfboard foam was the staple medium for surfboard shapers around as it was easier to work with and lighter in weight compared to the next best thing at the time which was
balsa wood surfboards.
EPS Surfboard Foam (Expanded Polystyrene) had been toyed around with by a few select shapers, but didn't really take off until the closure of the largest Polyurethane foam manufacturer (Clark Foam) in 2005.
Today, more and more surfboard brands offer models in both Polyurethane and EPS, with some even moving to 100%
EPS foam, as well as some blending the two such as
DHD and their new
Epoxicore construction.
EPS is lighter, slightly more buoyant and can feel lively in the right conditions. For more information, look into articles like
Poly or Epoxy, Which One is Best, and
Surfboard Construction Types which go deeper into construction methods and materials.