Many core choices are available to board builders. A quality craftsman will consider all options to find the one that will give both float and durability.
Surf Industry Foam Core Materials
Polyurethane (PU) foam - Most commonly used in surfboards. Poly is lightweight and shapes well using a full range of shaping tools from saws to planers to sand paper. This foam choice is thermosetting and glassed with a polyester based resin.
Polystyrene (PS) foam - Lighter in weight than PU, but more labor intensive to shape. PS is the weaker of the two but some of that gap is closed with epoxy resin. Important to note - PS is a thermoplastic foam and will melt if glassed or repaired with a polyester resin.
I am a blank slate - therefore I can create anything I want.
Tobey Maguire
Expanded Poly Styrene (EPS) foam - basically Styrofoam bonded beads. You likely know the strength of Styrofoam (think disposable coolers and packing materials). Though very light, EPS is very difficult to shape with any precision. Craftsmen generally steer far away from this core and it is usually reserved for boards shaped by a machine such - import boards and pop-outs. EPS also begins to gas out over time (especially at impact points) causing the shell to delaminate from the core of the board. (NOTE: There is a release plug on Stand Up Paddle (SUP) boards to vent off this gas periodically to stave off delamination.
Wood - Ochroma pyramidale, known as the balsa tree is a large, fast-growing tree. Balsa wood is a very lightweight, stiff material sometimes used in surfboard shaping. Multi-layer plywood, is sometimes used in skimboards; however, can be quite heavy. If used, it is usually found in beginner or imported skimboards.
Polyvinyl Chloride (PVC) Foam - structural PVC (like the pipe) foam. Waterproof. Light. Durable. This foam can be sourced in different densities. The higher the density the stronger the foam. This foam is finished with combinations of gel coat, polyester or epoxy resin and is used in skimboards, boat decks, boat hulls among other applications.
Surf vs. Skim - The Core Difference
Surfboards - The choice between PU and PS foams, is often driven by the Board Builder. Like any art, each craftsman will have a preferred medium (type of core) and the type of resin will be driven by that core.
Work Hard Surf Hard
Ricky Carroll - R& D Surf
It is challenging to find a Board Builder willing to shape EPS foam. That core is generally found in machine milled pop-outs.
Skimboards - Poly foams are sometimes used in skimboards, however are not the best choice. PU and PS can be glassed like a surfboard and will have performance and float, but not durability. The impact routinely dished out to a skimboard vs. a surfboard can make compression dings the least of your worries with poly foam.
EPS foam claims no fracture resistance and will also gas out, causing the board to crack and delaminate. EPS cores are usually found in import boards and, while sitting on a shelf waiting for purchase, they begin the gassing/delamination process and sometimes crack after only a few uses. These can sometimes be identified by the claim that a skimboard offers "seamless rails."
PVC foam is the top choice for skimboards. The dimensional stability will contribute float and balance. The fracture toughness of a high quality PVC core will deliver impact resistance. This explains why a skimboard can weigh under 7 lbs and support a rider weighing in at 200 lbs.
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