LOL its called poly fill and yes it does help quite a bit it make the bass seem a lil deeper to the ear not sure if it will make your number go higheer but it seems to be the case
walmart sells it in its arts and craft department under 5 for 1lb i think 1 cubes like .5 bag or .75 chit i put in the whole bag on my old sealed setup 1.5 cubes each chamber
It will probably make it sound different. It depends on your situation at to whether it will help the sound. If your box is kind of small due to space limitations polyfill will help the sound. Polyfill is used to make the sub seem like it has more air space.
my new box is like 3.3 cubes tuned to like 33hz and i put 3 pounds of the pillow stuffing stuff in there and im happy with the way the sub sounds, it has really good lows