Interesting. I experimented with several materials a few years ago, trying to make my own picks. I used cardboard (not rounf, but cut triangular pieces and rounded the ends with nail clippers). Biggest problem was longevity: I would go through several in a night's jam. They just wore out, got soft and were useless. True, they are inexpensive to make, but they don't last. Best material and closest to cardboard in flexibility was plastic. I used the soft plastic sides of kitchen containers for some good, durable picks. I tried using water bottles, but found them too soft without the stiffness I prefer. But ecologically, cardboard has a lot of advantages.