I cut up old clothing and fabric to stuff it. You have to cut it up and remove any buttons or zippers, the buttons and zippers or any hard objects can damage the arrow if they hit. Cutting it up increases density and insures no open pockets that will let the arrow slip through. I cut average strip sizes of abut 5"x12" or so, not real exact but I just went with a general size and I am only getting 6" of penetration from maybe 10' with a draw weight of 62#.

I think even with a 70# speed bow I wouldn't get much more than 8" of penetration so it is more than good enough for my setup.