pollyfill will make the subs react like they were in a bigger box but it do'nt make much of a difference about 1-2 dB's. pollyfill makes the airspace in the box denser then just free air, pollyfill alows air to pass through it but slower than if there was just "freeair" making the subs react like they were in a bigger box.
polyfill should help it sound a lil better, and make the sub think its in a bigger enclosure.. This works out for sealed boxes... but u cant expect a dramatic imporvement in loudness!