Spyder Foam

I scored a single billet of Spyder Foam - 2' x 5' x 2.75". Spyder foam is XPS manufactured by Dow - hence the blue color The foam is also referred to as Surfboard foam, but I don't know that it was ever a staple for that. It seems it's used mostly in RC aircraft wing builds.

This foam has a vertical grain structure rather than a horizontal grain structure which is found in the insulation version of the Dow XPS. The vertical grain gives the foam greater compressive strength - I've read propoganda that claims the compressive strength is twice that of the insulation version of the Dow Blue and 10 times that of EPS.

The higher compressive strength allows lower weight lamination schedules...I guess we'll see!

RC builder also use some EPP which is very durable. Expanded Polypropylene.
What about this?

Thanks for following along, Petr. EPP isn't a rigid foam, it's exceptionally durable because it bounces back whereas, EPS will break. I can best describe it as rubbery. I've only seen it in two densities a 1.3# and 1.9#. The 1.3# is what I think is used mostly in RC planes wings. It's almost impossible to sand and shape. It hotwires fairly nicely and I believe that's what the flyboy's do. It's molded foam and so has a skin, at least on one side typically - very similar to PU blanks - that are a higher density than the core. It needs to be skinned to even attempt shaping. It is used in some of the softop boards. The manufacturer will wrap a 3-6mm sheet of the EPP around a rigid core and then cover that with EVA or the vinyl shrinkwrap stuff.

I think I'll leave shaping that stuff to folks more patient than myself.

This stuff hotwires, but it's weird. It sizzles as it's melting - it sounds like bacon frying! The offcut also deforms it curved away from the core.

The foam is very rigid, it feels like it should translate into good pop when finished.

I'm not sure I like this stuff. It's not fun to shape.

With these slab-o-foam blanks, I measure the tail from the apex in the rocker. Mark and then transfer that to the flat deck side. Then just cut with a circular saw.

I think that this stuff reacts poorly to heat - the offcut curled away from the cut and I think the board developed a concave AFTER the hotwire.

I trace the outline and then cut that out with a jiggy.

Before shaping the deck, I shape the bottom contour. I had a devil of a time with the planer. I started with blades and that ripped huges chnks out. I swapped over to a barrel and that helped some, but still lots of ripping. Turning down the RPM's and using the barrel finally did the trick.

I mark the thickness at a few points. The tail, the back of the boxes, max thickness and then at the nose and freehand the dots.

I want to remove all the foam above the line, which would be a ton to mow with the planer. I use my hotwire bow and cut by draging it along the flat deck - that gives me a flat cut and I only need to focus on one line. I just get it close, I'll mow the rest with the plane.

All shaped, it went pretty smoothly, after the planer dealio.

The blanks weighs in at about 13.5 oz. Middle of the road.

XPS is copolymerized with polyethelene. You can smell it melting when it's being cut or shaped. NOTHING stick to PE and that is one of the problems with XPS as a core foam. I think another contributing factor may be with the way this stuff sheared off. I can imagine that under heel dents th foam can chunk, leaving little support for the glass.

The "generally accepted" method for laminating XPS is to scratch the surface with 40 grit and then laminate with extra resin that winds up filing the scratches. In effect creating more of a mechanical bond.

Hopefully I'll get to that tomorrow.

A regular lamination shop!

I did an eps side-by-side with the xps board, so that I could get a feel for the difference in laminating the two different foams.

The xps is closed cell and the resin swirl didn't sink into the foam, it just puddled. I had to spread it and it muted the colors. Also, the laps were a major PITA, the resin didn't soak there either and I really had to push to get the laps to stay down.

The eps was a breeze in comparison. Colors stuck and the laps were one hit. The xps wasn't impossible, but it's a challenge.

I tried laying down the purple 30 minutes before the white, a little better separation...but there is so much squeeqe work that everything blends together.

Poor man's perimeter "stringer"

Well, a worthwhile experiment. I've heard folks extoll the virtures of XPS, but in practice there wasn't anything stellar about it, IMO. It doesn't shape as well as EPS or PU. There wasn't any significant increase in pop or responsiveness over EPS, or if there was, it was so minimal as to be undetectable.

Compressive strength was good - Dennis at 280 didn't dent it with 4/4 on the deck.

Not something I'll pursue again.