split image largest slime making lesson

Once upon a slime, on 19 June 2022, 491 people took part in the world’s largest slime making lesson at Montreal Science Centre in Canada.

The slime students were taught by Yannick Bergeron, who is known as a "local slime star". 🤩

In addition to learning how to make the green goo, everyone also learnt the science of how it all works. Read on to learn how to make it for yourself! 🧪️

Largest slime making lesson students holding slime

Here's the slime-making recipe used for the record attempt (make sure an adult is around to help you):


  • A glass filled with water
  • Calcium chloride
  • Stirrer
  • Bottle of sodium alginate
  • Small jar


  1. Place the glass of water on a table.
  2. Add all the calcium chloride to the water and mix the solution well with the stirrer.
  3. Pour the sodium alginate slowly into the solution.
  4. Wait a few seconds for the chemicals to react.
  5. Using the stirrer, remove the strands of slime from the glass and place them in a small jar.

"Our slime recipe that we have been making at public events for years has broken a Guinness World Records title. It was so great!" - Christine Beaulieu, lecturer in the Department of Chemical Engineering at Polytechnique Montréal

girl holding up slime

How does it work?

Before we get into the science of slime-making, here are some useful definitions:

  • An atom is a tiny unit of matter, invisible to the human eye. Atoms are the building blocks for everything in the universe.
  • A molecule is two or more atoms joined tightly together.
  • A polymer is a large molecule which is made up of many smaller molecules joined together.

When the sodium alginate is mixed into the calcium chloride solution, the sodium atoms are replaced by calcium atoms.

The calcium joins all the molecules in the mixture together to create long polymer chains. This is called cross-linking.

Cross-linking makes the mixture more solid because the polymer chains become stuck together.

Sodium alginate is used in this way in some of your favourite foods, such as ice cream and fruit pies, to make them softer and thicker. 🍨🥧

kids creating slime

To achieve the record of world’s largest slime making lesson, 90% of all students must stay in the class until the end. But they can’t just sit around playing on their phones – every student must create the finished product by the end of the lesson. 🧪️

One of the people who helped organize this record-breaking lesson, Sara Arsenault, wasn’t sure whether they would be able to break the record: "What if the slime doesn't take? What if people left because the kids were tired?" 

GWR toy adjudicator in slime

However, once our adjudicator revealed the result at the end of the class, Sara could breathe a sigh of relief. 491 out of 493 students stayed until the end and they were all able to successfully create some slime. 😃

"Anything is possible with a good starting idea and organization!" – Sara Arsenault

Largest slime making lesson certificate