Got to patch my board again, which got me wondering about the construction.

Why don't SUPs use EPP (the stuff inside your stack hat) instead of EPS? EPP has better impact resistance than EPS.

Anyone know why?

Cheers,

Barrie

Kami uses it for his flex tail designs. Bodyboards are made with EPP.

Other than than, EPP is heavier, more difficult to cut, very hard to sand, and less rigid than EPS, so a very bad choice for encasing in glass layers.

The interesting foam is XPS because it is waterproof. But its slick surface makes it prone to delanimating (glass layer do not stick well). Some shapers have succes with it by roughing up the surface before glassing (sanding, punching micro holes, ...) .

Try to glass a bodyboard...

Seriously:
- XPS "blowing agent trapped in the cells expanding", no as it is a closed cell foam, nothing can come in or out the cell. So, if some air get trapped between the skin and blank, it cannot go back into the blank and by forcing its way between the sking and blank may create delamination.

- EPP SUP and surfboards actually already exist... they just aren't glassed. That's the beginner "foam boards". For instance sup-passion.com/stand-up-mousse-decathlon/ (note that it has an EPS core for ligthness and rigidity) Or the famous "Morey Doyle" www.vonweirdos.com/forsale/Original-Morey-Doyle-Soft-Board-_1040.htm

- EPP has no mechanical qualities for a sandwich construction between glass layer. You are better off just making hollow boards.

- Even if you manage to shape an EPP blank, it will never keep its shape for glassing...