You are looking at a Shrinky Dink. (You must now recite, in your best TV announcer voice: “Welcome to the MAGICAL world of SHRINKY-DINKS!!!”)
We discovered a pack of these things in the deeper recesses of our stored stuff, and thought it would be cool to play around with them and see if they were as much fun now as they were when we were kids.
It brought back memories of my aunt’s house, watching through the window in the oven door and waiting for the flat plastic sheets to start crinkling and shrinking. Still felt the same. Of course we weren’t doing Scooby-Doo ones this time around.
I’m thinking of illustrating a whole album cover on a Shrinky Dink sheet and baking it up real nice. I could take a picture of the unpredictably distorted result and use that as the actual cover. I am cackling with mad genius right now.