as said you need card... ive done alot of pep work... and found 200gsm card was ideal as its easily folded/shaped but still strong, and probably the miost acceptable thickness for the printer...
remember you need to take your printer into account.... i suppose you could get away wtih 160gsm or 180, but as i say i like working with 200.
using payer is simply a no no... i will not retain any shape, using cardstock the end product will usually support itself... we just ad inserts to hel keep the proper overal shape for when we resin/fibreglass!!
if you fibreglassed onto paper i can see it all just collapsing in to a heap lol!