PolyurethaneWhen you read about PU boards, you are reading about polyurethane foam blanks which are the most common blanks still among both daily surfers and pros. PU foam is easily shaped and airbrushed. Polyurethane foam is known for being more responsive in its performance but it also absorbs water and yellows (over time). Polyurethane surfboard blanks can be glassed with either polyester or epoxy resin, making it versatile in terms of giving riders more options. Polyurethane blanks are easily shaped thus making surfboards less expensive than Polystyrene since it takes less time to shape and finish each board. The most negative aspect of building PU boards is their impact on the environment since they contain carcinogens and are essentially impossible to recycle once in surfboard form. The big bonus: PU surfboards are the cheapest option.
PolystyreneWhile there are different degrees of Expanded Polystyrene foam, it is regarded as lighter and more buoyant foam than polyurethane. However, it is not as easily shaped and cannot be used with polyester resins due to temperature/chemical sensitivity. It does not react well to polyester resin’s hot chemical reaction and will melt. Therefore, epoxy resin is the only option with polystyrene. Many surfers, however, find epoxy/polystyrene boards have less “life” to them, lacking flex energy, which is probably why most of the top pros still ride PU boards. Polystyrene foam cores sealed with epoxy resin, however, last much longer and emit fewer toxic gasses, so the idea is that the combination is better overall for the planet. In my own experience, I find no real discernible flex energy difference when comparing EPS/epoxy and PU/polyester boards. However, I have ridden some EPS pop-outs that do lack the feel and dynamic curves and unique edges that make a surfboard seem alive, but in fun surf, it’s all good.
EPS VS. XPSYou have two main choices when it comes to Polystyrene foam. Open celled Polystyrene is beaded foam similar to a Styrofoam cooler, but the open cells suck up water if dinged. Besides the afore mentioned lack of flex and memory and high water absorption, another drawback is that open celled polystyrene is difficult to shape, paint or airbrush.
Closed cell polystyrene (called extruded polystyrene foam), on the other hand, is more expensive to produce but absorbs very little water and will remain white and “full of life” for much longer. Closed cell polystyrene is durable AND lightweight and said to be more flexible than expanded polystyrene foam surfboards, this containing that elusive flex energy. And similar to traditional polyurethane foam, due to its closed cells, extruded surfboard foam is easy to airbrush and paint but does often delaminate very easily because closed cell polystyrene builds gas that forces the sealed resin to separate from the foam. Epoxy Pro has developed “Thermovent” technology, which uses small vents that allow the gas to escape and thus avoid delamination.