Possibly a reference to the Trinia material...?
It seems that from a cost perspective it may not be as attractive however its machine-ability properties are similar to that of PMMA.
We have a customer who has used it. It has the texture of laid up fiberglass but I personally do no view it as a substitute for titanium.
The 'weave' of the glass layup appears to be fairly rough (not a super-tight weave) which would indicate to me there would be a reliance on the bonding resins to support the integrity or shape of the prosthesis.
I suspect that bars from these materials would also have a bit more play or flex in them which would, aside from any clinical issues allow lower quality less accurate machines (and robust CAM software & machining templates) being able to get away with more.
Just kind of thinking out loud. I'm sure there are much more qualified brethren here to voice opinions.