[Electrodynamic]

For subwoofer applications there have been reports of minor smoothing of the response curve, but I have never heard an audible difference.

If you stuff the enclosure with fiberglass (not just lining the walls) it can have an effect similar to polyfill. But polyfill doesn't itch, it stays in one place without glue, and it has less tendency to get inside the motor, and it does a better job at fooling the woofer into thinking it's in a bigger enclosure.