Surfing Explained: Ep10 Surfboard Materials EPS & PU Foam

It's our TENTH episode! What started life as a 30-second animation on noseriding has turned into this series. Thanks to everyone's support and comments so far.
This weeks episode of Surfing Explained we break down the construction of a typical foam and fiberglass surfboard. Starting with the stringer, we then analysis the differences between expanded polystyrene (EPS) and Polyurethane (PU) foam, then look at the fiberglass weights and polyester resin vs epoxy resin.
Enjoy!
Transcript:
In this episode, we’re going to break down the construction of a typical foam and fiberglass surfboard to understand the general concept and resulting qualities. In a later episode we’ll talk about some of the interesting alternative construction techniques and materials that are available, but for now, let's keep it simple.
A surfboard’s core is typically made from a plastic foam “Blank”, which is shaped into what might resemble a surfboard then covered by a skin of glass fibers and resin. Running through the center of the foam is normally a single strip of wood called the stringer, which adds strength and rigidity to the board.
Taking several materials, capitalizing on their qualities, and layering them up is known as sandwich construction (although within the surf industry we tend to reserve this term for boards with multi-layered skins). In a surfboards case, this construction style makes a structure like a steel I beam, and this contributes to the surfboards mighty strength to weight ratio. It’s the ideal system for surfboards as the inner core is thick, light, and buoyant, while the outer skin is thin, strong, and stiff.
When we look at variations in this construction method, different approaches will affect the weight, strength, and flex pattern of the finished board.
Depending on construction, the weight of a finished board is split about 50/50 between the skin and core materials. The stinger accounts for just a very small percentage of the final weight, but it’s the combination of the Skin and Stringer that accounts for most of the board's strength and flexibility.
Slide Title: Stringer
First off let’s consider the stringer as it’s the quickest to explain. Again, the stringer is the strip of wood that runs the length of a standard fiberglass board, and it's there because without it the board would probably flex beyond the tolerances of the core and skin materials. Essentially, it’s there to prevent the board from snapping.
With that in mind, it's obvious the stringer has an important part in determining how much the board will flex whilst being ridden - and although surfboards may feel very rigid, they can flex an amazing amount whilst you are onboard.
To increase the surfboard strength, especially on longer boards, the stringer width can be increased or more stringers can be added to cope with the increased stress,
and in the longboard era of the ’50s and '60s it wasn’t uncommon to have a three stringer board for maximum strength.
Stringers have been made from a variety of wood over the years, with plywood being most common for many years. Balsa and Cedar are also popular, along with regional woods such as Basswood or Redwood within the US. Balsa is a favorite nowadays on performance surfboards thanks to its lightweight, but shapers often opt for different varieties of wood-based on a particular aesthetic since the weight of any stringer is pretty low.
Using a strip of wood has its limitations; the main one being that the flex will vary depending on the grain of the wood - which is mostly hidden within the wood itself. A knot in the wood could stiffen the flex pattern in one area, potentially making the board more (or less) desirable to ride. This mightn’t be a huge problem, but if you want to make a copy of the board with the same flex pattern, all of a sudden you have something frustratingly unique.
Slide Title: Foam Inner Core
If you have ever snapped a board and investigated its contents, then you may be familiar with the inner core. Typically a plastic foam material, the core is mostly there to create the shape of the surfboard that the skin can be formed around, but it does also contribute to the overall strength of the board. By increasing the density or the stiffness of the foam we can strengthen the board without hugely affecting its flexibility.
Some pro surfers seek out lower density blanks with a lower weight for a high-performance board, or high density blanks with a higher weight for a big wave board - a tow-in board’s core might weigh as much as 5 times that of a normal board, allowing the rider to carry more momentum or be less upset by choppy conditions.
Polyurethane foam (PU) has been the standard core material since its creation in the 1950s.
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[@bonefishboards]

I've gone almost 100% to building EPS core (2 pound)/epoxy resins for the past few years for environmental and longevity reasons. I recycle all my EPS scraps; just took a load in yesterday. Epoxy has almost no VOCs. EPS/epoxy boards hardly dent. Built a 2 pound EPS/4,4x4 glassing test board and beat the snot out of it. No dents at all and I'm not a light footed surfer. And EPS/epoxy boards have a very long life. There are downsides to EPS/epoxy: (1) doesn't polish out to a new car shiny, (2) coloring the board is limited (e.g. resin tints do not turn out well; opaque pigments OK), (3) need to put a breather into the board to let out air/water vapor pressure to keep the board from delaminating. But at least one supplied has a great Gore-Tex valved leash plug that allows air to pass but not liquid water. It works great. The pretty, art-like boards you see are all PU foam/PE resins because it works better for art and color. But it's environmentally rough and those boards will not last as long, with all other things equal.

[@Surfmus]

@Andrew H 6lbs

[@surfnshowreviews7777]

This video is great... I love the simplicity and the breakdown is very educational. I am a visual learner and the animation is excellent. Thank you for putting these types of videos together for us surfers to learn more about surfboards and surfing. Cheers!!!

[@SurfSimply]

It’s our pleasure Surf n Show! Thanks for watching. I’ve just put the finishing touches to Fridays episode too, it’s covering longboard outlines, particularly the differences between wide point locations.

[@claytonadawag1662]

This video series is so helpful! Keep it up!

[@SurfSimply]

Glad you think so!

[@othman3192]

you covered everything that there is to know and you didnt take up much of my time, perfect!

[@SurfSimply]

I consider that to be the perfect compliment. Thanks Abizoman!

[@lukeacrey7571]

@@SurfSimply honestly I was just about to comment the same exact thing. Perfect video, nothing could have been explained and showed better 💯💯💯

[@XO-me9yb]

This one is super cool... awesome to know the differences

[@rs9196]

Best surfboard build explanation on KZbin. Big thanks!

[@Surfmus]

He missed a few things. Read my comment.

[@MrRickyrecon]

This video was awesome! Thanks for dropping the knowledge bombs!

[@MrLeeson660]

Amazing series! concise but thorough explanation 👍

[@SurfSimply]

Glad you enjoyed it MeLeeson!

[@IntuitiveReview]

awesome, thanks for the video!

[@craigphillips6496]

Your videos are THE best! Cheers!

[@SurfSimply]

Thanks Craig!

[@jimbosek5921]

Great job Will. I love these videos!

[@SurfSimply]

Thanks Jim!

[@DA-8956]

Amazing video!

[@NARQUELIN3]

gracias amigo !

[@luisaubriot772]

great, keep it up!!

[@SurfSimply]

Thank you Luis!

[@jessejamesb]

I've seen a few 3D printed boards out there. I think I'm going to have a go at it. Boards are too expensive in Canada and I have a lot of unused plastic. Looking forward to the hollow construction video

[@SurfSimply]

Print them and send us some prototypes Jesse!

[@tonybeatbutcher]

cool one !!

[@SurfSimply]

Glad to hear it Tony!

[@Seanh_lee]

So is epoxy pretty much stronger and more durable than a polyester resin board? Does it last longer as well? Thank you for the video by the way, it was super helpful!

[@MJKDESIGNer]

Very interesting

[@SurfSimply]

Glad you think so!

[@supaflip87]

Any suggestions for a layup for a high performance shortboard that is optimal for light weight and durability including less pressure denting? Let’s say your options of cloth are carbon, e-glass and s-glass in 4 and 6 oz options…

[@Surfmus]

I got a 6oz and 4oz on deck, double 6oz on bottom, in a light 1lbs (EPS), its is at 8lbs for a 6,7 board with huge volume at 44 liters.

[@bajaracer1]

Do you have a video that explains what makes the best noserider surfboard?

[@SurfSimply]

Hi Edan, yes there is one that discusses longboard outlines in the series. Thanks for watching!

[@SurfSimply]

kzbin.info/www/bejne/n2XIinh7eK9riMU

[@julesmorrissey]

👍

[@MysteriousOutdoors]

I am using XPS foam and want to float a gold dredge, I need your help .

[@tylerb1989]

can you go through lib tech construction in the next vid?

[@Surfmus]

7:00 is not easy, Epoxy is easier. 7:25 You can use Polyester resin on EPS. As long you seal it. Solarez sells a sealer. Also you can seal it nicely with a coat of Epoxy and can take Polyester afterwards, which is stupid because is like wearing a hat over a hat. I use what I have and to $ave though. But if used directly to the EPS foam, then use only Epoxy resin. You forgot to mention the need of venting the EPS foam regardless the density. It always off-gas, the hotter the ambient the worst. PU absorbs less water than EPS when an open ding is exposed.

[@JoseReyes-hu8zc]

nice

[@SurfSimply]

Thanks Jose!

[@yehudagoldberg6400]

Are 2 layers of 6 oz stronger than 1 layer of 12 oz?

[@SurfSimply]

Thats a fantastic question Yehuda which i attempted to research but could find any specific information on, sorry! My guess would be that 1 layer of 12oz should be as the chemical bond between 2 layers of 6 oz might be considered a weaker point than a single layer. But that is just a guess!

[@robertcain3426]

@@SurfSimply 2 X 6 is stronger than 1 X 12 everytime. Think of it like rope - small ropes entwined together. 3 X 4 ounce even stronger.

[@Surfmus]

Yeap!

[@eating1608]

hello there,always amazing contents.But what does "some tenth of a litre" mean?

[@RodrigoRosa]

i assumed it means "roughly 1L/10", so something around 100mL, which seems reasonable to me for a pressure ding.

[@rachgrigg2447]

Woaaaaaaaaaaaah lol way cool

[@SurfSimply]

Thanks Rach!

[@mathewwhittle10]

Am I first?... Nice!

[@SurfSimply]

Yes you are!

[@arthurvidal1180]

like 97% of people on this world i only understand metric system :/ sorry guys

[@SurfSimply]

Don’t be sorry, it is the surf industry’s units, not ours! Thanks for watching Arthur, I hope you found other bits interesting.

[@RoMpErStOmP3R]

“1 ft = 28.3168 litres so 28 litres = 2-3lbs” just use one system of measurement .why are you using 2 ffs🤦‍♂️

[@adonut4u]

you picked the wrong channel name lol