This is off my CM308D4's, the link explains each part of the Thiele/Small parameters for those interested in learning more about what they're dealing with of their own parameters better. 

Poly-fil by name is actually a brand and seems to have become more of an identifier of products than a single product, much like everyone pretty much calls any sound deadner material "dynomat" and its accepted as such despite over a dozen brands with other well known brand names. As such, Poly-fil fills the virtual area in the box by slowing down the sound waves, thus making the box seem larger. Breaking up soundwaves doesn't really make much sense. The commonly used phrase of "breaking up standing waves" which refers in acoustics to stopping reflections between parallel walls or similarly symmetrical reflective surfaces which cause tonal resonances; most often seen in square or rectangular boxes or enclosures.

As for the removed airspace, ideally in a sealed box application (2nd order enclosure), you should be able to increase power vs reducing the power. A ported enclosure would be different depending on anything else 3rd order and above.  I once had a Kicker rep tell me there was no actual difference in a Solobaric vs a Kicker Comp (at that time) with exception of the marketing of the two separated by the fact the Solobaric was sold as a woofer able to work in smaller enclosures, via adding power handling and the in the Thiele/Small/Parameters, the power was nearly doubled as the airspace was just over a 1/3 of a Comp needed airspace. Whether his comments were a 100%, I can't prove otherwise over 2 decades later but I've done well with both.