Teflon Tape Secret Messages

1. Cut a piece of Teflon Tape about 10 to 15 cm (4-6 in) long.
2. Write a secret message on the tape with the Sharpie marker.
3. Now stretch the tape from top to bottom, making your message taller, not longer.  Pull carefully so that you don’t tear your message. 
4. Suddenly you can’t read your message anymore!  Give the message to a friend and see if they can figure out how to make the letters their original shape again.
5. Just when they are about to give up, surprise them with a little science magic... Pull on the tape from end to end making the letters short again.
6. When you are done pulling the tape, your message will look normal again and your friends will be amazed.

Try writing a message on a plastic grocery bag. Now pull the bag from top to bottom, just like the tape. Does your message "disappear?" Pull the bag back from end to end. Can you read the message again?

Try to rip the grocery bag. Does the direction of the pull make a difference in the outcome?

How does it work?

Teflon Tape is a type of polymer called polytetrafluoroethylene (PTFE). That’s a really long word for a kind of polymer that has long chains of molecules lined up side-by-side and on top of each other. 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.

When you tried to tear the grocery bag, you also saw polymers in action. Pulling in one direction stretched the bag because you were stretching out the polymer chains. Pulling the bag in the other direction separated the polymer chains from their bonds with other chains in the molecules of the bag. That separation caused the bag to rip.