Fun, Messy Sensory Play with a Mentos and Diet Coke Experiment!

Exciting sensory play activities – like our favorite Mentos and Diet Coke experiment – can be fun, hands-on, and engaging without being complicated.

We’ve been launching soda geysers for eight years now, and it’s a backyard family tradition that never gets old! This hands-on activity is the perfect break from worksheets and screen time — just pure wonder and discovery.

Best of all, it gets kids asking the best kinds of questions:

Why do Mentos cause the explosion? Why Diet Coke? How does it work? Can we make it go even higher?

Konrad enjoying the shower of fizz and foam from the Mentos and Diet Coke geyser

Tips for an Epic Soda Geyser

After eight years of launching soda into the sky, here are some of our go-to tips for getting the most impressive and fun results:

1. Stick with diet soda.

Diet sodas (especially Diet Coke) create bigger geysers than regular soda. The aspartame in diet drinks lowers the surface tension of the liquid, allowing bubbles to form faster and shoot higher.

2. Warm it up.

Sun-warmed soda works best for us. (We do this activity on hotter days). Heat adds energy to the reaction, helping it blast even higher. We leave our 2-liter bottles out in the sun for a little while before the experiment.

3. Drop the Mentos in fast!

Speed matters. If the Mentos trickle in too slowly, you’ll miss the full explosion.

Our simple trick:

• Roll one note card into a tube (just big enough for the Mentos).

  
  

• Place a flat note card under the tube to hold the Mentos in place.

  
  

• When you're ready, hold the tube over the soda bottle, pull out the bottom card quickly, and let the Mentos drop in all at once.

  
  

4. Use 6 to 7 Mentos.

This seems to be the sweet spot for the biggest geysers. Too few, and the reaction’s smaller. Too many, and it can actually weaken the eruption.

But try different options! Experimenting with the number of Mentos is FUN and part of the process of learning what works best!

Konrad and Cannon awaiting the downpour of soda from the Mentos and Diet Coke geyser

The Science Behind the Mentos and Diet Coke Experiment

So, what’s really going on here?

Diet Coke is a carbonated drink, which means it contains carbon dioxide gas dissolved under pressure. That’s what gives it its fizz.

When you drop Mentos into the soda, something exciting happens. The surface of the Mentos is covered in tiny pits and grooves. These microscopic craters give the carbon dioxide lots of places to rapidly form bubbles. The sudden rush of gas escaping creates a massive burst of foam that shoots out of the bottle... our homemade geyser!

This reaction is a great example of a physical change. No new substances are created — just carbon dioxide gas being released quickly from the liquid. Because there are no new chemicals formed, this is not a chemical reaction, where bonds are broken and new materials are made.

It’s a great opportunity to talk with kids about the difference between physical and chemical changes. A chemical change creates something new. For example, when wood burns, it turns into ash and releases gases. But with our soda geyser, everything stays the same, chemically speaking. We’re just seeing gas rapidly escaping. That makes this a physical reaction, even if it looks explosive!

Why Use Mentos?

While it's fun to experiment with different candies, Mentos are the candy of choice for this soda geyser. They’re uniquely good at triggering a dramatic eruption for two key reasons:

1. Surface Roughness

Even though Mentos feel smooth to the touch, their surface is actually full of tiny pits and pores when viewed under a microscope. These imperfections act like bubble-starting hotspots, giving the carbon dioxide in the soda lots of places to form bubbles quickly.

The more bubbles that form at once, the bigger the eruption! Surface roughness of Mentos is important.

2. Density and Weight

Mentos are also dense and heavy compared to other candies. This means they sink to the bottom of the bottle almost instantly. As they drop, they disturb the soda all the way through, helping release carbon dioxide from the entire liquid — not just the top.

That full-bottle reaction is what sends the foam sky-high.

Other candies, like Skittles, Reese's Pieces, or M&Ms, have smoother surfaces and float or sink slowly, so they don’t trigger the same explosive reaction.

So, when it comes to soda geysers, Mentos are the way to go! However, experimenting with other candies for hands-on comparison is still fun.

Final Thoughts on Why the Mentos and Diet Coke Experiment is a Cool Way to Engage in Sensory Play

Science experiments like this one are a fantastic way to spark curiosity and inspire kids to explore how the world works. The Mentos and Diet Coke experiment is one of our favorite forms of sensory play—it’s exciting, hands-on, and always leads to lots of questions (and laughter).

For our family, this backyard tradition is more than just a fun spectacle—it’s a shared experience that fuels learning and strengthens our connection.

So, grab a few bottles of soda, a roll of Mentos, some notecards, and head outside. Get ready to turn curiosity into discovery with your own Mentos and Diet Coke experiment sensory play!

And if you're looking for another fun sensory play activity, check out our post on how to make Giant Bubbles with a homemade solution and DIY wand.

Check out this video from our YouTube channel to see our Mentos and Diet Coke experiment, a sensory play activity, in action!