Leak-Proof Bag Science Experiment

I’ve been having a lot of fun doing science experiments with my preschoolers over Zoom.  Part of the reason why is because unlike in the classroom where we do one experiment while a few children help and others watch, on Zoom calls they each have their own supplies and a parent to help them with the experiment.  My co-teacher and I have been trying our best to do experiments with items that can easily be found in everyone’s homes, that way no one has to go out to get supplies.  Today’s experiment was super simple and fun.  Before starting, have the children can make a hypothesis about what they think would happen if they poked a hole with a pencil through a bag full of water.  

On that note, I came across another fantastic experiment that I’m eager to try with the kids. It’s called the “Clean Water Experiment”. I love how it combines learning with environmental awareness, teaching children about the importance of clean water.

Engaging preschoolers in hands-on science experiments has been a rewarding experience, even through the virtual platform. Seeing their faces light up as they make discoveries and learn about the world around them is truly priceless. I can’t wait to see what other exciting experiments we can explore together!


-Sharp pencils
-Plastic sealable bag


Gather all the supplies. Make sure the pencils are sharpened to a point.

Fill the bag between ½ and ¾-full with water.

Seal the bag shut.

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.  You don’t need to be especially fast, slowly and carefully works well.

Repeat with the other sharpened pencils.

The science behind this experiment:  Flexible plastic is made of polymer chains. The polymers have many molecules inside of them. When the pencil goes through the bag, the molecules in the polymer chains surround the pencil, sealing it up tightly and preventing leaks. But when you remove the pencil, the molecules don’t move to seal the hole, allowing the water to escape.