Over at Unplug your kids, I read about how you can use #6 plastic to make shrinky dinks and wanted to give it a try. We salvaged some take out food containers and I bought some colored sharpies. The kids enjoyed coloring on the plastic, and I gave my hand at one. Wow, I haven't drawn for a while!
I'm not sure if it is the plastic we used or just that it was our first try, but they ended up sticking to themselves and not uncurling. I was able to pry one open and flatten it. It could have been that they were too large because the long skinny ones turned out a bit better.
I tried to make two of them into rings, but they wouldn't hold their shape. Still, this was a very fun project and I love that we can use what we would other wise toss out to make them.