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20 Minute Labs: The No Leak Bag

20 minute lab | No Leak bag | Yellow Scope



Now here's a great trick and a fun way to keep cool in the summer!

In this month's 20 Minute Lab, we'll use some household items to see how some forms of plastic are leak-resistant, even when you poke holes in it!

The supplies for this experiment are very simple, and it's a great one for a sunny day. It'll go fast, but you can extend the fun by experimenting with different materials to see what happens.


  • No Leak bag supplies | Yellow Scope bloga few round pencils (colored pencils are often round and work just fine! We happened to have double sided pencils, but that's not necessary)
  • pencil sharpener
  • plastic bag (a zip-lock style is easiest to handle)
  • water



    1. First, you'll want to stand over a sink or be outside in case there are any spills.
    2. sharpened pencils | Yellow Scope blogSharpen all the pencils so they have a good point on them.
    3. Fill the bag about half-way with water and seal it closed. Make sure there aren't any leaks to start!
    4. Now, if you're in a group, you might pause here. Add some fun anticipation by asking your friends what they think will happen when you pierce the bag. Make a hypothesis!
    5. Pierce the bag all the way through both sides with a pencil, leaving some of the pencil poking out on both sides. (Leave the pencil in the bag!)
    6. Observe what happens!
poke the bag | Yellow Scope blog



What's going on?

ldpe |Yellow Scope blogPlastic bags are made out of something called a polymer. A polymer is a type of molecular structure that is a chain of repeated units - like beads on a necklace. ('Poly' means 'many', so polymer means 'many' units.)

Most bags are made of a particular polymer called low-density polyethylene (LDPE), which has a lot of branching atoms on its chains of polymers. This makes it very flexible.

LDPE is a very common material because it is light, tough, leak resistant and inexpensive. Perfect for packing material and bags!

no lead bag | Yellow Scope blogWhen the pencil was poked through the bag, the long flexible molecules formed a seal around the pencil, so the water didn't leak out!

But if you try removing the pencils, the hole remains because the polymers were permanently squeezed aside by the pencil and can't return to the original shape. So when you're done, you can pull out the pencils to make a summer shower!

leaking bag | Yellow Scope blog

Keep experimenting!

Try these variations to keep the fun going:

  • a different type of bag (produce, grocery carryout bags, sandwich bag, etc)
  • try different types of pencils - bigger ones, smaller ones, the kind with flat edges, etc.
  • try pens, skewers, or sticks

What happens using these materials? What changes? What works best?






Let us know what you did. Share your photos and results with us on Facebook, Twitter, Instagram, or send us an email to We love getting your messages!

For more exciting experiments, check out our Yellow Scope Science Kits on the Shop tab of our website!


Chelsea Schuyler
Chelsea Schuyler