A surfboard is an extreme stressed skin structure. What I mean by extreme is that the limits of what is possible in a stressed skin structure are pushed to the extreme to get a product that is as light as possible and just strong enough for the job at hand. The skin part of surfboard construction consists of a reinforcement or reinforcements and a glue that holds it all together. In this post we’ll look at the glue.
Traditionally surfboards have been built with polyester resin. Polyester surfboard resin has been developed to be clear, non-yellowing, cure quickly, and be easy to sand. It is also relatively inexpensive. In case you missed it most of those attributes relate to the processing of the resin and ease of use but not on the quality of the finished product. Polyester resin tends to be brittle and weak, cracking easily when impacted or stressed. However despite these shortcomings it is dominant resin in the surfboard building industry.
Epoxy resins have a different chemistry and are generally better for flexibility, tensile strength, elongation, and impact resistance. Historically they have been quite a bit more expensive than polyester resins and have had some challenges with clarity, yellowing, and UV resistance. In the last couple of decades however the options for epoxy resins have increased with multiple formulations that are perfectly clear and resist yellowing either by being UV stable or having UV inhibitors added to them.
So while epoxy resins have better physical properties than polyester resins, especially in mechanical properties there are some reasons that they have struggled in obscurity in the board building industry. Historically it has been assumed that the consumer will not pay more for a surfboard. If you figure an average surfboard uses a gallon of resin, 20 years ago that gallon cost $10 and a gallon of epoxy ran $60-100 depending on the formulation. The weird thing is that over time polyester resin has more than doubled in cost but epoxy resin has stayed relatively stable (until 2021), additionally over time retail prices for boards has risen to make the added cost of epoxy less of a hinderance. Another huge reason that epoxy was not embraced sooner or in larger swaths of the industry is that industry processes were developed around polyester resin and working with epoxy requires some changes to technique and environment. This hurdle of processing differences still exists between polyester and epoxy board building but with higher demand for epoxy glassed boards in the industry more builders are beginning to use epoxy or offer epoxy as an option.
In my opinion a board glassed with epoxy is a superior board, it is much less likely to crack, either from flexing the board or dropping it, and has a much higher resistance to dinging and delamination. Epoxy can be used with either EPS or polyurethane cores. It is more expensive and somewhat harder to sand but given that the board will last longer I think the added expense to a board glassed with epoxy is justified.