As mentioned before by Leatheroo, X-ray film is a great medium for designing and saving patterns. It is strong, yet flexible and easy to cut. Since it's thick plastic it lasts virtually forever. About half of each sheet is transparent which facilitates tracing. Hospital X-ray departments throw away many sheets every day during start-up and calibration of the machines. If you have a friend in the medical field they can make inquiries, If not, a few kind words to an xray technician will enlist him/her to your cause. (you might even make a key fob in exchange and have a friend for life).