For my prototype I used the styrofoam cutter to make a back which I reinforced with dowel rods. On the backside is a strap made out of string in addition to a grip that is built into the styrofoam. On the top and bottom are two rails that the rubber bands can slide along, which hold the iPad against the high-friction backing. The rails are secured by three popsicle sticks which are inserted into the styrofoam.

This was my fourth design. The previous three were either too complicated, too weak, or not adjustable for size.