it will do little except to kill off some high frequencies making the room sound muddy(er).
polyester insulation can be used in some circumstances but generally you need heavier semi-rigid insulation to attenuate LF standing wave issues.
Not entirely certain I understand the question, but.... Polyester is a great absorber. You can certainly place Glass or Rock or other fibres behind it to create a deep and effective trap. But full area and not really worth doing anything less than 4"
I know it wont absorb any low frequencies.
My worry was that the sound wont go through the polyester cloth and therefore never really reaches the rockwool behind it? in which case the panel would be useless...
