The closure of Clark foam was a double edged sword. Clark had a formula that was designed for close tolerance blanks. The outer shell was the hardest foam, and the density dropped off towards the interior of the blank. OK for hand shaping. Not so good for machine shaping. â€œOver shapingâ€ would compromise the durability of the core. Today there are several PU foams available that are an improvement over the foam most of us used almost exclusively for decades. Lighter, tighter, whiter, and fairly even density into the core.
Expanded Poly Styrene (EPS)
also known as bead foam
Eps material has been around since the 50′s. Eps for surfboards came from large blocks of partially fused beads , primarily used for insulation and packaging. The blocks of foam were something on the order of 3â€™by 4â€™ by 12â€™. Blanks were cut from the big blocks with a hot wire. EPS must be glassed with epoxy. Early epoxies got a bad rap for being highly toxic if not handled right. They were also not very clear and tended to be more on the yellow or light brown side of things.
In the early 80′s a handful of board builders revisited eps. The foam hadnâ€™t really changed much. There was a lot of interest in EPS/Epoxy construction for sailboards. The strength to weight advantages were obvious in these larger watercraft. It became the go to construction for most of the custom sailboard builders. This know-how trickled into the surfboard world. There were a few new epoxies available that were formulated to work for board builders. These proved to be a little more user friendly and yellowed a little less that the boat resins that were used on early Styrofoam boards. Foam with larger (approx 4mm in dia) bead size was still hard to work with and the fusion between the beads was marginal. The ASP tour actually had an event in 1985 that was held in a wave pool in Allentown, Pa. Tom Carroll won the event. Quite a few pros ordered up lightweight epoxy boards for this fresh water event.
Now we are using surfboard specific eps foam. It is highly fused and has a much smaller bead size than the foams that were experimented with by earlier generations of board builders.
There are several surfboard specific epoxies available. They are easier to work with, have much better clarity, and if handled properly, are safer.
Is Eps more buoyant?
2 boards of equal volume and area, if one is lighter, that is basically your gain.
With EPS cores it usually works out to a 10 to 15% difference. and feels much livelier when surfed.
Eps foam requires glassing with epoxy resin. Epoxies are much more durable than polyester resin. They also come in a variety of flex matrices and the combination creates a very durable, light weight surfboard.
What are the differences between the two?
PU is considered an open cell foam (counterintuitive) and is basically a plastic foam filled with irregular gas bubbles. When a PU core is expose to water, it takes a while to migrate and over time the foam will also deteriorate.
EPS is considered an open cell foamâ€¦think many tiny ping-pong balls stuck together. The trick is to compress and fuse the little beads together so water doesnâ€™t have the ability to migrate freely.
PU can be glassed with either polyester resin or epoxy. In fact, PU with an epoxy glass job is a much more durable alternative to the poly.
EPS must be glassed with epoxy.
What about dings?
With EPS/epoxy boards, small dings where there isnâ€™t too much of the core material exposed, it is ok to use a quick acting UV cure poly. Solarez does make a UV â€œEpoxyâ€. For larger wounds, you need to use epoxy. Polyester resin will melt the EPS foam.
What about flex?
EPS foam glassed with epoxy resin is not stiff. If anything, all else being equal, it will be more sensitive and have quicker springback than a PU/PE board. In fact, because of the lightness/buoyancy you can go thinner if you choose, which will make the board feel more alive. Epoxies also come in a variety of flex matrices and the potential to tailor flex to personal taste is wide open.
Certain types of molded EPS/epoxy boards have a layer of high density sheet foam sandwiched between the core, cloth, and resin. This is what causes those types of molded board to be â€œstiffâ€ feeling.
When deciding on which core material to use, consider your local conditions.
In everyday surf, smaller weaker waves, light wind, the lightness and liveliness of EPS/Epoxy should be a no-brainer.
For larger more powerful surf, and locations that have wind exposure and surface issues, PU is probably a better choice.
A board with a PU offers a quieter, more dampened feel when compared to EPS.
Why donâ€™t you see more EPS in the stores?
Cost: Part of it is price point. The cores donâ€™t differ much in price. Itâ€™s the epoxy resin that is more expensive and through-put time also affects costâ€¦itâ€™s a little harder to work with and takes longer to go through the factory than PU/Poly.
Cosmetics: Epoxy is also more likely to â€œyellowâ€ or discolor a little more quickly than polyester. The EPS stays whiteâ€¦the epoxy discolors. The opposite is true of PU/Poly
Mythpercetion: the surf media perpetuates the notion that the tour pros donâ€™t ride EPS/epoxy. What the media usually forgets to mention is that the pros do have unlimited access to very light, very fragile, PU/PE boards. To weigh in at about 5lbs, a PU core needs to be glassed with single 4ounce cloth, top and bottom, with maybe a 4oz tail patch. Good for anywhere between 2 to 20 sessions. A 2 lb EPS core can be glassed double 6oz top and single 6oz bottom and still come in at close to 5lbs and have a much longer lifespan than a comparable pu/pe board. A lot of our team riders do use EPS, especially for smaller, weaker surf.
Commitment: there are not many board makers that have embraced this type of construction. It is challenging to learn how to work with these different materials but the reward is worth it.
Virtually everyone who has custom ordered EPS has been stoked and when it comes time for a new one, itâ€™s not even a question.