This is a really exciting experiment that you can try at home with your kids. Try it outside or over the sink just in case!

You will need:

  • Sealable plastic food bag
  • Sharp pencils
  • Water


  • Fill your bag around half full of water.
  • Gently poke a pencil through one side of the bag and out the other end
  • Leave the pencil in and add another one to the bag
  • Keep adding pencils until the bag starts to leak. Our record is 24 pencils!!
  • At the end, remove a pencil and water will start to squirt out.
  • Test this experiment with other sharp objects e.g. knitting needles and different bag e.g. shopping bags.
The Science Bit:
Plastic bags like these are made out of polymers! Poly means ‘many’ and ‘mers’ means molecules and polymers are long chains of individual molecules, called monomers. When you puncture these bags with a sharpened pencil, you’re essentially separating polymer chains without breaking them. The long chains of molecules than squeeze in tight around the surface of the pencil preventing any sort of leak.  

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