Paper: Unknown 24lb. Flyer Paper (about 20" x 8.5")
A classic -- the hard part is finding one-sided paper [rimshot].
This one is a bit old and battered. I folded the corrugations onto a couple different sheets of paper, then cut them into strips and reassembled them with some tape. The loop was made while the paper was flat, then the corrugations were put back in. It's a bit tricky, especially at first.