The boards are built like an aircraft wing with a spar and ribs made from marine ply as a frame.  This frame is covered with a skin of Paulonia boards 6mm thick.  Paulonia is soft and light like balsa.  The rails and rocker are shaped with a plane , and then the board is sanded, sealed with marine varnish, and ready to surf.  The Paulonia is plantation grown in northern Australia so the whole board is eco-friendly and requires only some wood, glue and varnish (no fibreglass or resins).  They surf great.  Thanks to Rob, Gary and Darren at Tree to Sea for the workshops on how to build these boards.