We live outside of Seattle so we know a lot about 2 things; coffee and rain.
This is a fun experiment to test different materials to find out if they are water proof or not.
Gather your materials. You will need several plastic containers or cups, duct tape and materials to test. Suggested materials could be clothes, plastic lids, aluminium foil, wax paper, construction paper, grocery bag.
Tape the material so it's covering the opening of the cup. to weigh down the cup you can pop a rock inside . Leave one topless.
Put it out in the rain or by your sprinkler if you have only blue skies.
Wait until the one with no cover is at least half full. Remove covers carefully and compare.