Access......, as in it is extruded polystyrene from big box stores designed for wall insulation, that anyone can get. It is junk, that delaminates like crazy. Those of us that have been building composite boards for decades, played with lots of extruded polystyrene (XPS) over the years. You can get fairly decent white XPS that works Ok for surfboards, but it expensive, sort of heavy, and has out gassing issues. All extrude polystyrene outgases, warps and delaminates when it gets too hot. The blue, pink, and yellow stuff (dow, owens) is light, but not strong, and has terrible memory reflex. Instead of returning to it's original shape, once bent, it remains in the bent form to a large extent instead of springing back to shape. Notice, that basically no one in the thousands of manufacturers of high performance surfboards uses this stuff as blank material. It can be useful for foam stringers or other aspects, that are not necessarily crucial but it is not a good structural core material. When you buy cheap boards you get cheap materials.

Nick