Leak-Proof Bag

Supplies

• Zip-lock plastic bags (good quality, medium size)

• Sharpened pencils (round, not hexagonal works best)

• Water

• Jug or bottle for pouring

• Tray or bucket (recommended, just in case!)

Safety First

• This experiment can get wet — do it over a sink, tray, or outside if possible

• Ensure pencils are sharp but handled carefully

• Staff to demonstrate first before children try

• Remind children not to squeeze the bag while pencils are inside

Steps

1. Fill the zip-lock bag about half full with water.

2. Seal the bag tightly, checking there are no leaks.

3. Hold the bag over a tray or bucket.

4. Slowly push a sharpened pencil straight through one side of the bag and out the other side.

5. Observe that the water does not leak out.

6. Repeat with more pencils if desired.

7. When finished, remove the pencils over the tray and pour the water away.

What to Observe

• The bag seals tightly around the pencil

• Water stays inside the bag

• Multiple pencils can go through without leaking

Explain It Simply to Children

“The plastic bag is stretchy. When the pencil goes through, the plastic stretches and seals around it, stopping the water from escaping.”

Discussion Prompts

• Did you expect the water to leak?

• What do you think would happen if we squeezed the bag?

• Would this work with a blunt pencil?