Cotton flox in resin

I have a question some of you Epoxy builders might know. Is Cotton
Flox okay to use as a structural filler in vinyl ester resin?. And if
so, why is it not called for to be used in it? Mostly, micro balloons,
cabosil, and milled fibers are used in vinyl ester, but in epoxy they
use cotton flox. I can think of a few uses where cotton flox would be
nice to use. I'm just can't find any info say whether or not it's
compatiable with vinyl ester resin.