Teflon Tape is a type of polymer called polytetrafluoroethylene (PTFE). If you try to stretch the tape end to end before stretching it from top to bottom, you won’t be able to stretch it much at all. That is because the polymers are bonded to each other very tightly. But, there are lots of chains stacked on top of each other. These stacks make it possible to pull the tape from top to bottom and stretch your secret message. When the polymer chains are pulled from top to bottom they slide over one another and reduce the number of chains in a section without breaking the chains themselves. When the tape is pulled back end to end, the chains are realigned and your message is legible again.