Made some 4foot by 2foot acoustic panels got them setup in the room, and wow what an improvement for under 60 bucks. The imaging is so much better, same with the detail, and clarity. Also the bass is tighter.
near the walls, I used mineral wool as the absorbtion material, and use polyester batting as to cover so the mineral wool material doesn't get in the air. Though still trying to decide what I want to use to cover them to make them look nicer. That also won't affect there performance.
You could also use fiberglass, you should be able to find absorbtion rates of different materials online.