Pencil Piercing a Bag of Water (DIY Leak-proof Bag)

pencil piercing water bag

Let’s say, you are having a plastic bag filled with chocolate milk and on your way to school the plastic bag a stick poked. And, the bag started leaking. Would you enjoy the leaking of bag? I am sure you wouldn’t. How can we make a leak-proof bag? Read further on this DIY Leak-proof Bag article and see how a bag holds water even after you pierce pencils through it. Please note that this DIY Leak-proof Bag article is not intended to make a leak-proof bag. It only demonstrates how a bag of water escapes leaking after it is pierced with pencils. 

Try it yourself

You need:

  1. A plastic bag (zipper bag is good)
  2. Some water
  3. A few sharp pencils
  4. An adult to supervise

What next?

Step 1: Open the plastic bag and pour in some water, almost up to half of the bag.

Step 2: Use the zipper to close the bag tightly.

Step 3: Now take pencils one after the other and start piercing the zipper bag. You can pierce through the water surface. Repeat until all the pencils are pushed through the bag.

Are you scared to do it? Don’t worry, your plastic bag won’t let you down.


In DIY Leak-proof Bag, the water won’t spill even after you pierce several pencils through the water filled bag. Why is this happening? There is no magic in it but pure science. The long chains of molecules in the plastic bag automatically close the gaps and seal around the pencils. As the bag gets sealed around the pencils quite faster, it won’t let the bag to leak out water. If you liked this experiment, do not forget to read our other experiments and lessons.

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