Well, as title indicates, what does EPP mean, stand for...

Many thanks

Martin

Expanded PolyProplyene (spelling might be off)

This is opposed to "EPS" -> Expanded PolyStyrene.

Basically, the foam is made from a different plastic.

EPS foams are generally more rigid, are attacked by solvents, usually (at least in the extruded form, not the beaded form) have a more "closed" cell structure, and when compressed/damaged, they do not recover. EPP foams are usually floppy, can take certain solvents such as Goop glue which attack EPS, have a coarser, more open cell structure (which makes attaching things to the foam a challenge, sometimes- you need to use more PU or spray glue for a given task), the big benefit of EPP foam is that it will recover from compression. If it gets hit, it will bounce back. EPP is used in automobile bumpers for this reason. If it tears (EPP tears more easily than EPS), once it recovers, you can PU glue the hole for a repair. An all-EPP wing tends to be too floppy for combat unless it has a stiff skin, such as the Predator series which rely on a stiff covering such as Ultracote or icarex to stabalize the wing. In some cases you will see an EPP leading edge (which generally takes more impact damage) glued to an EPS core, this is a "best of both worlds" construction that gives damage recovery along with rigidity. This construction is used in the Falcon/Cobra series, I believe, as well as the sscAVENGER. Some core cutters such as RA and Aerowright offer optional EPP LE core sets.