In this section of board design I am going to explain the differences between these two materials. First off, both have advantages and may have a place in your quiver. But saying epoxy or poly is vague in terms of exactly what we are talking about. Many people think epoxy is tantamount to an eps/pvc/epoxy sandwich construction (popularized by Surftech). In fact epoxy is simply a resin and implies nothing about a board’s make-up, other than what kind of glue is used. WIthout getting into the chemistry of the two main resin types used in surfboards, epoxy is undoubtedly a superior material to polyester. It is however more expensive and difficult to use. Polyester is quick and easy to use, so it’s no wonder that the guys who build boards prefer it by far. Epoxy is generally a lot less toxic, although some people are allergic and cannot work with it.
The way that resins influence constructions is that they have varying compatibities with other materials. For example, polyester melts polystyrene foam. Epoxy however, does not, and allows the use of lighter weight core materials. Using lighter cores enables the use of heavier glass, which can make a board a lot stronger. A thin layer of epoxy resin in four ounce glass isn’t that much stronger than polyester resin in the same fabric. But when you double up six ounce glass and saturate it with epoxy, the result is impressive. A demonstration I love to do is to take an EPS/epoxy board, hold it about four feet off the ground and drop it on concrete. People are always shocked by the fact that I would dare to do that to a new board, then just as surprised when the board is unscathed. The properties of the materials that allow one of these boards to largely escape dings are the following: first, epoxy has greater elasticity, greater fatigue strength and greater tensile strength than polyester. That means it’s harder to break and doesn’t go dead as fast. Polyester has the tendency to fracture, resulting in those spider dings you get when you bump your rail against something hard. You will never get a spider ding with epoxy. Another reason epoxy boards are tough is the core material we use.
The main cores we use in surfboard construction are polyurethane (acronym PU, traditional), expanded polystyrene (EPS, aka styrofoam), and extruded polystyrene (XTR). There are other alternatives, none of which are ready for contemporary high performance surfing. Polyester can only be used with polyurethane foam. Epoxy can be used with PU, but the resin is slower to harden and tends to soak into the foam too much, resulting in a heavier board. Because of this, I believe that polyester is the best resin for PU foam. With EPS and XTR we must use epoxy. I’ll talk a little more about their physical properties before moving on to what you really care about, which is probably how they work. The downside of EPS and the upside of XTR is their permeability by water. EPS is bead foam, so if you get a ding, you’d better get it fixed, because water travels freely between the beads. It is true that some foam is fused better than others, limiting water migration (Marko), but none is completely hydrophobic like extruded polystyrene. You can get a ding in your XTR board and it will never soak up a drop of water. Polyurethane soaks up water, but it will not go too far into the board past the point of entry. The elasticity is a big difference between polystyrene and polyurethane foams. if you push on polystyrene, it springs back, while you get a permanent dent in urethane. However, polystyrene is more rigid and will snap before polyurethane will. An epoxy board seems more likely to break clean in two, where a poly might get a destructive buckle. Still, an epoxy board glassed well is quite a bit stronger and harder to break than a poly.
One last thing to discuss is Surftech style sandwich construction. It is a misconception that these are simply molded “pop-outs”. It is actually a ton of work to make one of those things. First they shape an eps core, glass it, then vacuum bag a layer of pvc foam around it, shape it again, glass it again, fill it with bondo, sand it, paint it, and clear coat it. It is such a labor intensive process that there is no way to cost effectively make them here in the US. Firewires are more or less made like this, also in Asia, sans the paint and bondo, but with wooden rails.
So how do they work? Epoxy boards are lighter, faster, stiffer, more buoyant, more responsive, and stronger. But they are also “pingy”, “poppy” and sometimes overly sensitive to variability in surface conditions. Poly boards flex more and better dampen vibration, resulting in a smoother, flowing, more organic connection to the wave. People who like epoxy may think pu’s feel dead. But there is a functional reason that world tour surfers overwhelmingly ride polyurethane/polyester constructs in competition. That said, there are a lot of top level surfers who prefer EPS boards. Slater seems to ride them pretty regularly, for example. Which is best for you? If you boil it down to the basics, you have to ask yourself what’s most important to you. Is it price? Is it feel? Weight? Durability? There is no one answer. Some people like epoxy and some like polyester.