It’s another smart publicity stunt from Elon musk. The surfboard were designed to fit inside or outside the Model S, X and 3 electric cars. The Tesla Surfboard has an EPS core and uses a bio-based epoxy resin instead of polyester.
Epoxy is superior to polyester. Epoxy is stronger and more elastic than polyester. Using epoxy for surf board is not new and has been around for over 15 years.