I think just about most packaging plastic works for this. We used berry containers because we seem to collect them. I preheated the oven to 300 degrees.

I cut up the containers into random pieces and handed them off to the kids to decorate.

They added color with permanent markers. When they finished I punch a hole in each one.

We laid the art on a baking sheet lined with aluminum foil and placed it in the oven, keeping our eyes on it the entire time. This literally takes about 15 seconds. They curled up and I pulled them right back out.

Some of my holes were still useful and some we couldn't even find, so another try with the hole punch was needed.

We used some string to hang out beautiful plastic art from the trees in our yard. The kids love asking friends if they can guess what our art used to be.