You can use the stuff that they use to fill plushies, but you have to compartmentalize it to keep it from shifting around. I'm assuming you are talking about the body and not the head. The thing is that stuffings make washing extremely difficult. If you are talking about the head, I suppose you could use some sort of plushie type filling, but it would be hard to keep it shaped properly. I built my fursuit head on a kickboxing headgear. I just wipe the inside of it out with a soapy cloth and I'm done. Cleaning is spot cleaning only on the outside. You don't want to use bean bags or anything that could possibly go rancid or "bad" with sweat. You also have the problem with the weight. I have a heavy fursuit. It weighs 17 pounds, not counting the head. If you add bean bags to that, it makes it a real task just to wear it around.
