Demonstrate how polymer chains work together to prevent water from leaking out of a plastic bag. Plastic bags are made out of polymers, which are long chains of individual molecules, called monomers. When the plastic bag is punctured with a sharpened pencil, the polymer chains are separated without being broken.


  • Sharpened pencils
  • Zipper-lock plastic bags
  • Water
  • Paper towels


  • Make sure the pencils are sharpened to a point.
  • Fill a zipper-lock bag between ½ and ¾-full with water.
  • Gather hypotheses. What would happen if you pushed a sharpened pencil through the water-filled bag?
  • Holding the bag in one hand, use the other hand to slowly, but firmly, push one of the sharpened pencils through one side of the bag. Make observations.
  • Repeat with the other sharpened pencils.
  • Once finished, hold the bag over a sink to remove the pencils.