The vast majority of “surf style” wakesurf boards are made from EPS foam. We’ve read sales details from ocean surfboard manufacturers that show Polyurethane is still the most popular core foam in the ocean. Ad you no doubt are aware, a single manufacturer controlled most of the production of Polyurethane blanks, used in surfboard manufacture and he suddenly shut down operations without warning. Surfboard shapers sort of scrambled to find alternative sources for blanks and also alternative materials. EPS foam was one of the materials that made a significant inroad into surfboard blank market and surf style wakesurf production joined that change. Skim style boards are mostly made from Divinycell, well the high end boards are.
So EPS is a funny foam, it’s comprised of a bunch of small hollow beads all mashed together. Inside the beads is a blowing agent and air. To make this post less laborious, lets just call it AIR. So those beds are like tiny little tennis balls. A thin shell of plastic and thien inside it’s all air. In fact, EPS foam is MOSTLY air. Now when we say “mostly” we are talking something like 98% air in many cases. So 2% plastic and 98% air. That’s WAYYYYY mostly air. You can also get the idea, it’s probably not very structurally sound. AIR and really all gases are compressible, you learned that in your 5th grade science class. Solids and liquids aren’t compressible, but gases and air in particular are. All foams are basically some form of solid material, usually plastic and then air or soe type of gas. The air that is trapped inside the plastic helps give it a lighter weight and also allows the foam to compress, somewhat. Higher density foams are made by changing the ratio of foam to gas.
So a higher density foam would have MORE plastic and LESS gas than a lowers density foam of the same materials.
What is it about air, and gases in general, that allows it to be compressed? In comparison with solids and liquids, the individual particles (atoms or molecules) of any gas are quite far apart from one another, with nothing but a vacuum in between them. Therefore, when pressure is applied to a gas, the particles can be squeezed closer together.
So EPS foam must simply be amazing stuff to be used in wakesurf boards! No, it really is shitball foam. It was principally designed to be used as wall insulation, and cheap wall insulation at that, but it was one of the alternative foams that was made popular when urethan blanks became scarce.
Here is a fun little demo. Let’s apply some compressive forces to a chunk of eps foam and see what happens.
Right? That’s some force! Can you guess what happened to the foam under the truck tire?
It gets mashed to about half it’s original height and then the tire tread is left in the top side of the foam. BUT did you notice what didn’t happen? It didn’t break apart, did it? The underlying EPS beads all got smashed and deformed, but somehow they seemed to stay stuck together. So EPS foam’s sort of magic is that it can get squashed, but stay together. So it’s not really structurally sound, but it’s light and doesn’t break into a gazillion pieces with extreme compressive forces. Some other foams, when faced with this sort of force fail by crumbling into a gazillion pieces, so that’s not a great thing either!
Ok, so lets apply that to some linear PVC foam. It’s hard to see, but it’s a small chunk under the front wheel.
It’s a little hard to see, but there is some deformation, but also a small piece broke off at the leading edge of where the tire rolled over it.
That’s pretty common with linear PVC foam. It’s brittle and it will deform under extreme compressive loads.
Now, outside of skim style boards, divinycell / cross linked PVC foam is used as a skin, but it’s actually designed to be used as a core material in composite sandwiches. The reason is that it offers great shear properties, it bends and deforms really well! BUT and this is important, it doesn’t typically lose it’s shape or at least not much.
Are you confused?! We’re sorry, the point that we are making is that the strength and durability of wakesurf boards isn’t in it’s core, it’s in the exterior lamination. It’s the glass job that makes the difference! That’s really true of ocean style surf boards and skimmers all over.
EPS foam was not a great choice as a core for anything, it was originally designed as wall insulation. BUT, as EPS foam became more viable as surfboard foam, manufacturers like Marko and WNC started refining the processes focusing on making it more suitable for surfboards. Rather than focusing on getting as much air inside for insulation purposes, the focus became getting more beads and plastic stuffed in the same space (surfboard) and aligning the bead walls to improve compressive forces. 1 pound foam still kinda sucks. It’s just hard to do much with a foam that is 98% air. BUT what firms like Marko and WNC were able to do is improve compressive strength with EPS foams in the 1.5 thru 1.9 pound density range. AND that’s why we switched from the old school 1 pound density foam core. Luckily, we build and test all of the boards that Flyboy Wakesurf constructs. We know and understand vacuum bagging and as you’ll see in this build thread, we use it all the time.
We don’t rely on someone else to tell us how something should be built, we know and we develop the structures. We’ll be honest, we’d prefer that you trust us that think we are 100% perfect all the time. Lord knows we aren’t but we test and build and refine AND fail a bunch. So that when we settle on a construction, it’s because we couldn’t get it to fail.
If you’ll refer to the pictures above, when we ran over the two separate foams we did damage. So now lets do the same thing to our newest composite structure that James has been riding for about 3 years, we’d guess.
That isn’t the best picture, we actually rolled back a few more inches but can’t seem to find the picture. BUT you can see that there is a ton of weight on the structure. AND this is the result!
Pretty much unscathed. Now, we’ll go into the details of the construction as we detail the build out, but the core is a molded 1.5 pound density and the exterior is laminated with fiberglass, epoxy and bamboo veneer. The process that we use to laminate the veneer to the EPS core allows the load to be dispersed over a much larger are. So the EPS foam gets to do it’s thing as being able to compress and compact, but we spread that load over a much larger area so the foam doesn’t fail in compression. As we mentioned in a previous post, bamboo is stronger than mild steel in the same thickness. We’d also like you to take note that we used a relatively small section of this composite structure, compared to the other test samples. It basically does it’s job very well that we can get by with a smaller cross sectional area.
It’s kinda nifty!
A few things to take away, one is that we stay on the leading edge of developments in foam makeup, because manufacturers like Marko and WNC are always improving. Then we work with their improvements to enhance our own construction. As we said we only use the best materials in manufacturing. It’s a ton of work and and it’s not cheap, but we believe that it results in the most advance products and really keeps us relevant in terms of technology. It’s something YOU can trust. Also, we test and refine and do it again and again. There is almost the constant state of development in EPS foams, epoxy resins and the various reinforcement materials. We literally are obsessed with keeping up to date with those developments and employing those that make a substantive difference. You simply can’t rest on your laurels or rely on someone else to dictate how you’ll make something.
Thanks so much for following along, we really appreciate it!