You can also use the plastic that is used for yarn sorry don't know the correct name, their are also the boards for handbags or if you know someone who can cut, you can use 2 layers of cord board. When I make my tote bags I use Shape Flex on both the outer and inter fabric, fleece interfacing iron-on attached to the outer fabric and, utility fabric and then quilt. This works for me that I don't need to put anything else in the bottom it stands up and strong.