SRPP fin build

I’ve been testing a new material:

SRPP: Self Reinforced PolyPropylene

This is a composite where both the matrix (resin) and the fibres are PolyPropylene.

It is the same material that samsonite uses for the new suitcases (branded as “Curv”):


I found that sanding the stuff is extremely hard! I used a random orbit sander and it took me forever to sand these guys, and they still don’t look smooth. I tried 60, 120 and 240 grit pads.


So I would not recommend this material for building fins, but I wanted to share this.


So now the pics!


finFoil Output and fin panel:


Layers routed (of double foiled test):


The double foiled:


The single foiled:


Single foiled left, double foiled right:


And a special layup still to be tested with Textreme carbon inside (



Tough stuff.  Thanks for posting.  

Hi Hans,

That is interesting.

In the final pics, it looks to me like the surface is still a bit rough / pitted, I assume because of the difficulty of working with the material.

Are you going to glass over them or anything to smooth it out?

A side note: my old Bosch random orbit sander had a little rubber belt underneath the disc that kept the spinning under control.  I learned that when this was removed (or broken from age and use), the disc would spin very fast and remove material much more quickly - not good for fine sanding, but helpful when a disc-sander wasn’t available.

Wow, looks like a tough slog. The photos of routed pannels seem to show that as this material heats up it becomes very pliable and elastic. Sanding by hand must’ve been a total clusterf**k Hans!