Here are some materials from around my home. Perhaps you have some similar to use in your investigation?
I am going to investigate whether or not they are waterproof by dripping a little bit of water onto each one very carefully, and seeing if it soaks all the way through to the table. If it doesn't soak through that means it is waterproof and would make a good rain hat for Puffin!
Look carefully and feel each material before you drip water onto them. Can you predict which ones might be waterpoof and which ones might not be?