Plarn is yarn made from plastic shopping bags. You know the ones, they collect under your sink and in the cabinet and you swear your going to use them for something someday. You can use them for wastebaskets or carry your craft projects around in them but there's really only so many you can use. (Unless your moving and can't find enough boxes, don't laugh I did that once)
Anyway here are some links for making plarn and crocheting with it.
I usually cut mine 1 inch, but otherwise here's how to make it
Plarn makes great shopping bags that you can take with you to the grocery store. The problem with this is you don't get more bags to make plarn with!
Round Plastic Bag Tote
How about handbags?
Plastic Hobo Handbag
Green Tote for Earth Day