Most efficient (best) Dampening material for Sealed/1.2cu/Fiberglass/IDQ-12 v2 ?

Hey guys, the title almost says it all. I recently purchased a custome built sealed fiberglass box for my e92 bmw 335i and i want to know what kind of material to put on the inside of the box. The box was too thin when i first got it so i added like 4 more layers of fiberglass matt and then a nice thick layer of KITTY HAIR so im guessing the 1.2 cubes the box originally was is around 1.1 or 1.0 now. So now i was wondering what would be the best material to put on the inside of the box to make my IDQ-12 v2 sound the best. by sound the best i mean have the tightest, cleanest, most crisp bass. Increased bass wouldnt hurt either

Ive heard of all sorts of stuff like Egg Crate foam, Studio foam ($$$), Fiberglass insulation, Polyfill, etc and i dont know what to do.....

I also hear alot of people saying if you put "XX" in the box then it will trick the sub into thinking it is in a larger enclosure? im not sure if i need that?

thanks guys, i really appreciate it.

 

forgot to mention i will be using a zapco 500.1 amp