I have used both fusible pellon and that works pretty well. If you want it even stiffer, you can use peltex, but it is expensive. Best to buy it at Joann's when you have a 50% off coupon and buy a bunch of it. I also use peltex for the bottoms of my bags, where I cut two pieces the same size and fused them together with the iron and then sew back and forth in a small triangle pattern to reinforce the piece. Then I create a fabric sleeve to cover it and sew it into the bottom of te bag.