This is the question that Year 2 tried to answer this week.  We tried different materials by putting them over a measuring cylinder and securing them with a rubber band.  We then used a pipette to drop water onto the material to see whether they were absorbent or waterproof.  The metal foil was waterproof and so was the plastic.  We decided that plastic would be more comfortable to wear though.  We definitely wouldn't use paper to make a raincoat.  This was so absorbent that it went all soggy!