These are the number 6 plastic lids we used. Number 6 plastic is often found on top of bakery and deli foods.
These are our decorated Shrinky Dinks, prior to melting. Place the plastic on parchment paper. You will want to watch them the whole time they are in the oven--the plastic melts so quickly that it's fun to watch the changes take place. Plus, you don't want it to be in the oven longer than necessary.
These are our creations after they melted. The plastic shrinks a lot and thickens (as seen below). Finished shrinky dinks are about 30% of their pre-melted size. We had the most success with the smaller pieces (2-inches or smaller). Larger pieces didn't uncurl after melting--the edges melted to the middle.
Although I originally got this idea from my mom, you can visit this Skip to My Lou post for additional ideas for your Homemade Shrinky Dink creations.