I wanted to make a bio filter using a soda bottle, air, and some sort of media. I used suction cups attached to the bottle to hold it in place. Rubber bands were used to hold the airline in place. ( the rubber bands seem to rot very easily) Looking around I found at "The Dollar Tree" store small hair rollers that had a plastic covering with what looks like round tipped fingers. I pulled the cover off the roller and cut them into small sections.
The fingers stuck to each other not allowing for circulation of the sections. I turned all the sections inside out. This worked and I had a working bio filter.
I wanted more surface for filtration so I again pulled all the media out, cut many more up turning them inside out. Some of these I put inside one another sometimes putting three together. They look like little bio spears. The picture does not show the finished media very well.