Any 100% polyester batting that isn't chemically treated is fine. I use both the pillow batting or the quilt batting in different types of filters. Potscrubbers are good and many have a sponge inside them. I like them more for wet/dry filters as cheaper bio balls. Lava Rock makes fine, cheap submerged biomedia if you need a lot of it and don't want to pay the premium for ceramic media. Lately I've been using baked clay oil absorbent in UGFs/plenums and BCBs, that works great and it's cheap.
