HD Foam, will either of these do?

My local Lowes only carries these two types of foam insulation:

Insulfoam Epanded Polystyrene


And Dow RS Styrofoam


Can I use either of these for epoxy construction? I am planning on skinning the board top and bottom with 1/8" Okoume Marine Plywood, then a layer of 6 oz, and I have a small amount of 1" thick Divinycel that I was planning on using for an internal stringer and the rails. Foam prices here are really getting out of hand and I’m hoping to fill the lower stress areas of my board with cheaper foam.


I have used the EPS Insulfoam, but it was only 1#. It surfed, but i wouldnt try it again.

IMHO with 1/8" plywood on the outside you can use any kind of crappy EPS on the inside as the plywood will distribute the load.

I have made a few boards out of both. The “blue” foam, if its what i think it is, will be of a higher density. Is the EPS white, and seems quite soft? If so, this is probally 0.5 lbs or 1 lbs eps. If you are skinning the blank with the wood, you should be good with one layer of 4 oz, You want to use at least 2 layers of six, probally 3 if its on the rails if you end up using the EPS on the rails. The blue foam, you could get away with 2 layers of 6 oz.

Try a test panel for the rails, and see how happy you are with the strength. I have never used Divinycel, so i can’t comment. Maybe someone else can.

Using epoxy, your good with both. I have had no problems. People may mention gassing, to solve this, i vent all my boards (all are eps/Dow foam…XPS maybe??), and try to keep them out of direct sunlight during storage.

Have a good one. dave

I gave both foams a quick “pinch” test and the white EPS is definitely softer than the blue foam, but the white EPS is available in a wider variety of thicknesses.

Divinycel is similar to Corecel and is a very dense foam that I’ve used before to shape kiteboards. Unfortunately, a sheet of 1/2" Divinycel costs about $200US locally, so I’d like to use it where it will do the most good.

I plan on ripping strips of Divinycel for the rails, the HD foam is so soft I don’t really trust it there. Plus, Divinycel shapes very nicely with a sureform and sander.

One more question: Besides using a hot wire, any other methods for shaping this HD EPS foam that work well?

“besides using a hotwire”…

I was surprised how well a long thin fillet knife made clean precise cuts, even curved ones on both blue and white foams in question.

Oneula and I have used both foams and I don’t like either.

The insulfoam is the cheapest, it’s easier to shape and glass, but I’ve had more problems with fin boxes with this foam than any other. If you do glass on fins and Okoume skins it should be OK.

The blue dow foam is harder to shape and is supposed to out gas, so there is a possibility of delams. On the plus side. it supposed to be more waterproof than the insulfoam.

The insulfoam floats better, so you can go thinner than the blue dow, it’s also lighter. You don’t need a stringer if you make a compsand. Solid wood rails or wrapped rails will be plenty strong. I have the soft insulfoam boards with both types of rails, and no stringers. We think that wrapping the skins around the rails with a layer of glass under that is faster and stronger than doing the solid wood rails. It’s just harder to do it really good especially with a thicker or harder skin.

Howzit SharkCountry,

Thanks for the info, especially the info about the Insulfoam. The board I’m planning is a kiteboard that will be roughly 1 inch max thickness. The only reason I’m thinking about either of these foams is because the price of Corecell and Divinycel (what I normally build kiteboards with) is just ridiculous. I’ve got a hunk of Divinycell that I hope will last for at least 2 boards.

There won’t be any fin boxes (I’ll be using “wake board” style fins that are bolted through the deck) but I will need to install threaded inserts for the foot straps. I plan on reinforcing these areas Divinycel and/or solid wood (maybe redwood or cedar?).

My plan is to make a foam core with a 1" x 3/4" thick divinycell “stringer”, with wide strips of Insulfoam on either side of that, then cover top and bottom with 1/8" Okoume ply, and finally wrap the rails with a strip of 3/4" x 3/4" divinycel. Then I’ll probably vacuum bag a single layer of 6 oz top and bottom and epoxy.

Last question, did the insulfoam you used have aluminum foil on both sides? Apparently that’s the only way it comes here.

You’re going to have compression issues with either foam especially with a kite board.

What I would do is make a 5 ply sandwich using






make a ripper on a table using a fixed horizontal hotwire setup that you can slide your 1" EPS through to get two 1/2" eps sheets. Then build your sandwich in bag using the 1/2" EPS sheets.You can add on EPS around the edges once you build your sandwich core and cutout your outline. Then you can shape your rails and glass it all togethor.

If you want to do those heavy kiteboard concaves on the bottom then add another 1" layer of EPS on the bottom layer and shape your concaves into that before building out your rails. Most of the punishment(pounding) will come from the deck side.

Almost all the kiteboard builders I’ve heard of are build their boards out of only Dcel or Qcel foam since they are inherently thin. There are other options but they are all more expensive like NIDACORE.

Personally for regular composite sandwhich surfboards I’m hooked on bluedow

true it has outgassing issues

but the weight and the ride are closer to PU in feel than anything else I’ve tried.

It’s easier to finish shape and has a stiffer and quicker snapback when reinforced with wood skins

For my personal board experiments it just suits me fine

You can actually build a matrixed hollow plywood-only board using this technique from Tree2Sea

No foam required just plywood and alot of cross members. If you follow Paul you can probably cut the whole thing out using a sharp box cutter.


The insulfoam at the local Lowes has a thin plastic wrap. The blue dow costs almost twice as much as insulfoam here, so for us insulfoam was a cheap alternative.

I think that Home depot’s foam is a little better because it doesn’t compress as much and the heat from the curing epoxy doesn’t melt it like the lowes insulfoam. We’ve had problems with that foam melting more than any other. It can also compress on heavy impact. I think the epoxy wood skins have a little give so they flex, but then may feel a little soft where the core has compressed. We’ve vacuumed lowes insulfoam and found that it came out of the bag very compressed. The blue won’t do that, but I’ve read that it will delam under heavy impact. I haven’t used my blue foam board in heavy conditions, so I don’t know how it will hold up.

Maybe my brother will jump in here and give you his thoughts. He’s the mad scientist, I’m igor.

FYI… CMP was making tow in boards with EPS and balsa that were pretty solid. He also used Okoume panels in high stress areas.

This isn’t my first kiteboard project. I’ve made about a half dozen over the years, including a 4 ply sandwich not too different than you’re recommending. That board was way too heavy and stiff (flex is also a desired quality in some kiteboard designs), although admittedly, that board was virtually indestructable. My last couple of boards were all made with a single sheet of 1/2" Corecell and 2x 6 oz top and bottom. These boards were bullet proof (in fact I dropped one of the boards in the garage the other day, it fell about 6 feet directly on its rail, bounced about a foot, but no dings!). Not to say there isn’t any compression with this foam, but it isn’t really a big issue (remember we use thick, soft foam pads under our feet also). I’d build my next board this way also, but $200 for a sheet of 1/2" foam? Too rich for me!

Since the board will only be about 1" thick at its widest (and tapered to about 1/2" at the tips) I’m not really thinking about building up a wood framework core. Way too labor intensive for this project, I’ll save that technique for a “real” surfboard.

I hadn’t really thought about the “gassing” issue, and I really don’t want to have to put vents in this board. Its likely to be underwater a fair bit during use so I’d really rather keep it sealed up. I like the idea of building with different densities of foam though, just seems pretty “techy”. :wink:

Ooo… melting, compressing and gassing? Not exactly what I wanted to hear. :frowning: Even though I’ll be doing this on the cheap, I hate to spend a couple hundred bucks on glass, epoxy and vacuum bagging materials only to have the thing delam a couple hours later. Hmmm… I’m gonna have to rethink this. Another option is to maybe just build a D-cel fishbone frame, no EPS, and skin it with 1/8" ply and glass (maybe 3x 6 oz?). So essentially make it a hollow board. then I’d have to put vents on it… hmm… guess there’s no easy and cheap way of doing this…