Depending on the fit and finish of your bag material, some filling products may work better than others. Some prefer something malleable, others need weight and firmness. I've tended to use some 6mm plastic BBs from my airsoft days that have held up pretty well, i can shape the bag(s), but they're rather light. Nice when carrying them around but you can scoot them on occasion. I've gotten used to that and like being able to adjust that way sometimes.