It's one of the most common dilemmas within the surfing community. Is the surfboard I am holding laminated with epoxy or polyester? Here's how to tell.
Let's start by keeping it in simple terms.
So, short answer first. Epoxy resin is normally used to glass surfboards built on expanded polystyrene (EPS) foam cores.
On the other hand, polyester resin is normally used to laminate boards built on polyurethane (PU) foam.
EPS and PU are the most widely adopted surfboard foam cores. Epoxy and polyester are the outer shells.
Despite some outer resemblances, the two paradigms look and behave differently.
Time to read the signs below and learned how to identify most boards on sight and by touch. It's actually easier than you might think.
What epoxy and polyester are, in plain words
First things first. What exactly are these two fundamental resins used by surfboard shapers?
Epoxy and polyester are two types of liquid plastic used to seal fiberglass cloth to a foam blank and make the finished surfboard hard.
Epoxy cures when two parts are mixed together and makes a tough, flexible shell. Polyester resin is mixed with a catalyst and hardens into a thinner, stiffer shell.
Both lock the fiberglass to the foam, but they do it with different chemistry.
Quick visual checks
If you're in a surf shop, there's a simple visual method that helps distinguish between the two components.
Look at the label or stamp first.
Many modern boards are marked EPS, Epoxy, PU, or Poly. If the blank is labeled EPS or the builder lists epoxy construction, it is epoxy on EPS.
If the board is advertised as PU, a PU blank with polyester resin is likely.
When you cannot find a label, use the checks below.
Weight and float
Pick the board up or watch it float. It's a good trick, this one.
EPS epoxy boards tend to be lighter for the same volume and sit a touch higher in the water, whereas PU polyester-coated boards usually feel denser and sit lower in the water.
But why does this happen?
It's because EPS foam is lower density than typical PU blanks, and the epoxy layup often uses more volume under the glass. Most surfers notice epoxy boards paddle easier in small surf for that reason.
The knock, flex, and feel tests
Another detection method is to tap the deck with your knuckles.
EPS/epoxy often sounds a lighter, slightly hollow note. PU/poly often gives a heavier thud.
Also, press the rail and push the nose. Epoxy/EPS models are usually more springy and can feel a little stiffer and more lively. PU/poly boards tend to flex in a slower, more muted way.
Remember that these are not perfect tests, but they work more often than not.
Look under the glass and at the stringer
You may also check the end of the board where the fiberglass meets the foam, or look inside a ding.
Traditional PU boards nearly always have a single wooden stringer running down the center. EPS blanks often have no wood stringer, or they use thin stringers, foam stringers, or carbon patches and rails.
If you see a full-width wooden stringer deep in the foam, the blank is almost certainly PU. If you find a hollow core or a foam-only core with carbon tape, it is likely EPS with epoxy.
Ding behavior and repair clues
Cracks and crevices never lie.
When the board is dinged, the broken edges reveal its inner secrets. Polyester resin repairs often look more brittle and yellow with age. Polyester also gives off a strong styrene smell when sanded or broken.
Epoxy repairs are usually harder to sand smooth, but do not chemically attack EPS foam.
Important rule, though: do not put polyester resin on an EPS core. Polyester chemicals will dissolve or "melt" EPS foam and can make the damage much worse.
Epoxy resin is safe to use on both EPS and PU for repairs. When in doubt, epoxy is the safer repair choice.
What the glass job looks like
From a surfboard maker's perspective, polyester layups are often thinner, with a slightly softer, less glossy finish when aged.
Epoxy layups tend to retain clarity and look thicker or glossier under new paint.
Over time, UV exposure can still yellow either system, but many builders and surfers realize epoxy tends to stay clearer longer.
Remember - looks can be altered by tint, paint, and extra coatings.
A few practical identification steps you can do right now
- Check for stamps or labels first;
- Lift and compare. Lighter, floatier board could be EPS/epoxy;
- Knock the deck. Hollow or springy sound points to EPS/epoxy;
- Inspect the stringer. Solid long wooden stringer usually means PU/poly;
- For a ding, note smell and the reaction of the foam. If the foam crumbles, yellow, or smells strongly of styrene, that is a polyester system and PU foam. If the foam is very white and foamy and the resin will not burn it, that is EPS/epoxy;
- When you must repair, and you are not sure, use epoxy resin. It will not chemically attack EPS, and it bonds well to most foams. Never use polyester on EPS;
Words by Luís MP | Founder of SurferToday.com
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