Introduction: Pencil-pierced Bag That Doesn't Leak! Try It Now!

Picture of Pencil-pierced Bag That Doesn't Leak! Try It Now!

Ever wondered what would happen if you pierced a plastic bag with a pencil and left the pencil in it? Would it leak or not? Read on to find out!


To investigate if a pencil-pierced bag with the pencil still in it will leak.


I think that the bag, once pierced by the pencil will leak or rupture.

Step 1: Materials Needed

Picture of Materials Needed

Materials Needed:

Plastic Bag (Sandwich bag, Ziploc etc...) ...................................................................................x3

Pencil (Any cheap "traditional" pencil that can be sharpened.) ...................................................x1

Water (Try to use a bucket or bowl to collect the water if the bag ruptures, to save water) .........*

Bucket or Bowl (To collect water if the bag ruptures)...................................................................x1

*Various amounts.

Step 2: The Test and Results.

Picture of The Test and Results.


  1. Fill a plastic bag about three-quarters full with water.
  2. Position the plastic bag over a bucket.
  3. Pierce the bag with a pencil, leaving the pencil in the bag.
  4. Observe whether it leaks or not, and if possible please comment below about how it went.

Results. (See the photos above.)

I conducted three trials, each time I filled each plastic bag up to the roughly the same level and asked my assistant to hold it as I pierced the bag with the pencil. On the first trial, the entire bag ruptured, however for the last two trials, the pencil held and no water leaked.


The experiment proved my Hypothesis wrong, as can be seen in the images. However, I had loads of fun conducting the experiment and taking photos of it... ;)


A more scientific explanation/conclusion:

The water pressure in the bag presses the plastic tightly against the pencil, forming a water tight seal. However, if the pencil pushed too slowly or with too much strength, the plastic will stretch and there will be too big of a gap to create a water tight seal. Another factor would be where the pencil penetrated the plastic bag, if it was too high, then there would not be enough pressure to create the water tight seal, if it was too low then there would be too much pressure and would result in water leaking through the hole.

Step 3: Extra: Using It As a Party Trick... & Special Thanks

Picture of Extra: Using It As a Party Trick... & Special Thanks

I know this was supposed to be more scientific centred, but this would be such a great party trick. So I tried out with friends and they were absolutely amazed! They said it was just like magic! As long as the bag doesn't rupture (it takes a bit of practice... (: ) you can do the trick anywhere! Please vote for me in the competitions I have entered, Thanks!

Special thanks to my ever-helpful assistant, VanessaMcL !


saverello (author)2014-04-04

nice idea but the science behind it lacking - why does it work? Is there a trick?

wesleykxm (author)saverello2014-05-23

Yeah.... The pencil stays in place, because the pressure from the water in the bag pushes against the it and holds it in place and thus the pencil prevents any water from coming out.

RedVelvetBows (author)2014-03-17

I tried it and it never ruptured! *magic man*

wesleykxm (author)2014-03-09

Thanks! I hope I will be able to post more Instructables like this in the future....

hunter999 (author)2014-03-09

Neat idea, I quite like this! Thanks for sharing :D

emilyvanleemput (author)2014-03-01

I did this once with a balloon and a skewer :) So much fun :D

That sounds like fun too! :)

wesleykxm (author)2014-03-02

The first time I did it quickly and the bag tore, However, I pierced it slowly for the two successful trials, so doing it slowly definitely works better

雷达 (author)2014-03-02

You very smart ,l like this,┏ (^ω^)=☞

brandt e (author)2014-03-01

did you pierce is slowly or quickly?

wesleykxm (author)2014-02-28

Sounds great! Hope the kids you show it, enjoy it, try to post some pictures of it if possible!

Psycho4Ever (author)2014-02-28

Wow made this in school, when I was eight, and totally forgott it till now. Thanks alot for the reminding! This will totally become a part of my "science"-projects with kids to wake there interest in science and knowledge.

About This Instructable




Bio: Hi! I'm Wesley, I'm a 15 year-old teenager in China, I like photography, technology, programming, tinkering and unicycling.
More by wesleykxm:Quick-Release Paracord Camera Wrist Strap w/ GIFEasy 5-ingredient Honey marinated chicken!Super-Easy 5 ingredient Apple Crumble Pi(e)
Add instructable to: