Jan 16

EPS foam for Wakesurfers

We scored major on some EPS foam that we think we can use for wakesurfers and we wanted to share that with you and also take a moment to explain how EPS foam is made and the various flavors it comes in.

What we found was some .41 pound nominal density EPS foam. It’s the lightest stuff we have ever handled. Moving it into the shop, it actually felt like walking a kite, where it wants to fly away! We’ll get into the details more in a minute, but this stuff is ridiculous!

Everyone that is reading this has seen EPS foam. It’s often erroneously called Styrofoam, which is a trade name held by Dow Chemical for XPS foam. EPS foam is found in everything from coffee cups, the containers for your leftovers at restaurants, coolers, packing peanuts, etc. The list goes on and on and on. If you have every examined say a coffee cup made from EPS foam, you’ll notice it’s white color, but also what looks like little beads that comprise the makeup of the foam.

Those beads are the result of expanding small granuels of plastic polystyrene. This expansion of the granuels is called pre-expansion. Here is the start of the process. Small amounts of polystyrene are mixed with what is referred to as a “blowing agent” typically pentane gas. These granuels are then subjected to a steam bath, which causes two things to happen the heat melts the polystyrene and the heat also causes the pentanae gas to expand. Those granuels then become what are called “beads” of eps foam. They aren’t connected at this point, they are just plumped up and await further processing, much like a thanksgiving turkey.

The beads are sorted and classified by weight and size. For clarity, let’s assume that the smallest bead sizes are classified A and the largest are classified C. Now, if all of the beads were made from granuales of the same amount of polystrene plastic then they would all be of a uniform weight, just different sizes. The technology isn’t quite that accurate, so wholesalers of EPS beads typically sell 4 grades classified based upon density and the bead diameter. There are tons more specialized EPS beads, fire retardant and things like that, but for most applications there are just the 4 grades. After the sorting the beads are allowed to age, that process is called matuartion. That process isn’t all that long, typically 3 to 24 hours. Not like fine wines!

So in the process we have all these tiny beads and now we want to create a final product from them, like coffee cups or a cooler. The beads are introducted into a mold and again heated. This final molding a heating causes the beads to expand yet again, sometimes as much as 40 times their original size and as they do, they start smashing together in the molding process. The heat that is applied, also causes the beads to melt and with the pressure applied, the various beads stick together.

You can see that there are a few ways to affect the final density of the finished product. Higher density beads is one, a bunch more of the smaller beads placed in the mold, etc. Bead size and density both play a role in the density of the final product.

In a very real sense, EPS foam is like a random honeycomb, the little beads are hollow and attached. What would be the best size bead for just such a honeycomb? You can imagine that if it was just 1 giant bead the size of your board, it would be mostly air and so very light, but not very sturdy, right? One tiny hole in that giant imaginary bead and it’s toast. So a larger NUMBER of total beads in the final product increases the durability. That is it can withstand more abuse before becoming toast! More beads to break, gives a greater longevity. BUT, more beads would normally mean more weight and that is the most common formation. Higher density foam will have what looks like smaller beads jammed together.

A┬árevolution for wakesurfers! Ok, not. ­čÖé We had to, it’s just so much fun to spam like that. What we found in this foam is the smaller beads, but they are also of a lower density. It’s pretty uncommon and a tad bit pricey. What we are hoping, is that it will give us a weight savings, but also increase durability! That would be great news, even if not revolutionary.

Let’s spend some time calculating the density of this block of foam. The first step is easy, we’ll weight the sheet of foam and it nets out at 6.3 ounces. That’s not the density, because density is a unit of measure based upon a standard 1 cubic foot. That is to say, 1 pound density foam is actually 1 pound per 1 cubic foot in density.

Super light foam 002

6.3 ounces! Stupid light! So the next step is we have to determine the total voulme of foam we are working with. To make it comparable, we want to convert all measurements into feet, so that our final number is that same pounds per cubic foot density.

We’ll show you some pictures to document it, but it’s approximate dimensions are 23 inches wide, 64 inches long and 1 1/8 inches thick. EPS foam is graded in 1 cubic foot standards, so 1 pound density EPS, which is REALLY light, is actually 1 pound per cubic foot in density. We have this weird sheet of foam, so we have to CALCULATE the relative proportion to a cubic foot in order to arrive at the density.

Sorry for the upside down picture, but you can see the width is just a shade under 23 inches

Super light foam 004

It’s LONGER than 48 inches, by this 16 inches. We hope you’ll trust us on this, so the 48 + 16 is 64 inches long.

Super light foam 005

Here is one last picture to give you an feel for the overall length of the sheet, it’s longer than a wakesurf board.

Super light foam 009

So let’s do some math! We want to convert all of the measurements we have in inches to feet. So we divide them all by 12 and the results come out:

23 / 12 = 1.91666 feet for the width. 64 / 12 = 5.3333 feet for the length and 1.125 / 12 = 0.09375 feet for the thickness. By multiplying all of those together we’ll get the cubic foot measurement of our sheet of foam. 1.916666 x 5.3333333 x 0.09375 = .95833234. So not quite a full cubic foot, but really close.

Knowing that 1 pound per cubic foot density would be 16 ounces exactly, we would expect our .95 of a cubic foot sheet to weigh 15.333184 ounces. We know that our sheet of foam is only 6.3 ounces, so a reasonableness check would have it LESS than 1 pound density! In fact, 6.3 / 15.333184 puts us in the range of .41 pound per cubic foot density!

Now normal EPS foam density for wakesurfers is probably minimally 2 pound and most is heavier. In our previous sandwich construction, we have used 1 pound density, so we are looking forward to seeing if we can use this sub 1 pound density EPS successfully for wakesurfing. We’ll start talking about the conceptual changes needed to use this crazy light EPS foam as a core material.

Thanks so much for following along, we really appreciate it.


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