Do a Google for Chopper Gun. Basically they chop a yarn of glass and
blow it into a stream of polyester.

Choppers are not the best method for a DIY builder. A chopper gun rig
is not cheap and takes a fair degree of skill to set up and use
properly. If the mix is not perfect you end up with an uneven cure
and greatly increase the probability of blistering. The layup is
weaker so it has to be thicker and heavier than hand layup.

Choppers are loosing favor even in the low end mass production area
because of polution laws. Spraying polyester produces large amounts
of VOCs floating around. If the EPA dosn't come down on you for
violating half a dozen laws the neighbors definitely will. It is just
less expensive to use a more modern closed mold layup method like
infusion than pay for all the equipment needed to stay legal.