Do-It-Yourself Rubber Stamp Project
5. Trace the Bottle Cap's Circular Outline onto the Foam
You're tracing the bottle cap on the foam so that when you draw your design onto the foam. you will be sure the design will fit on the bottle cap.
Notice that I'm using leftover scraps in the photo above. This is a good "second life" use for little scraps of foam and discarded medicine or drink bottles with caps.