The first is in the 6th edition of Vance Dickason's THE LOUDSPEAKER COOKBOOK. In this he determined after extensive testing the the most attenuating stuff between acoustistuff, pillow fill and fiberglass was fiberglass. And the most effective density is 4 lb cu ft. There are some caveats but they don't apply between 500hz and 4500 hz.

The second is a study sponsored by Rod Elliot on his site that showed the effectiveness of the insulation is dependent on the size of the filament. Pillowfill and acoustimass ar int he vicinity of .05 mm and fiberglass is .01. Acoutical fiberglass is even better at .005.

Marlboro