Carbon fiber is used when you need high strength + least weight possible, and expense isn't too much of a concern (which is why it's pretty much exclusively used in the aerospace industry). For pep, the little bit of weight it might save you is just not worth the expense IMO. Carbon fiber cloth not only costs like 2x as much as regular cloth, but it also necessitates the use of a vacuum bagging system in order to squeeze out excess resin. Pep also generally requires so much additional finishing work on the surface with bondo that I can't imagine why anyone would bother. It MIGHT be feasible if you're casting from a highly detailed mold, but you couldn't do something like a helmet, and vacuum forming with styrene sheets instead would still be much cheaper.