Pop Rocks Expander – Candy Science

Discover the secret behind the famous popping candy by mixing Pop Rocks and soda.

If you are a candy enthusiast, like a lot of the people at Spangler Labs, you know that not all candies are created equal. And, if we're being honest, Pop Rocks are one of the greatest candies of all time! You dump a few of the tiny pebbles onto your tongue and, in an instant, they begin fizzing, popping, and snapping about in your mouth. What's going on here? Being scientists, we devised a way to figure out the popping secret behind the famous candy. Are you ready to expand your mind (as well as a few balloons)?


  • Pop Rocks(try to find multiple flavors)
  • Balloons
  • Funnel
  • 12-16 oz bottles of soda?(the greater soda variety, the better)
Watch the Video.



  1. The first item of business is to get an entire package of Pop Rocks into a balloon. You might be able to carefully pour the candies into the balloon's mouth, but we have found that it's much easier if you use a small funnel. Place the narrow end of the funnel into the mouth of the balloon and empty the Pop Rocks packet into the funnel. Make sure all the candies are in the balloon by giving the funnel a few firm taps.
  2. Place the balloon over the mouth of a bottle of soda. Careful! You don't want the Pop Rocks to drop into the soda before you're ready. Stretch the mouth of the balloon over the mouth of the bottle, but make sure the valuable candy content of the balloon doesn't dump into the soda.
  3. Are you ready? Grab the balloon and dump the Pop Rocks into the soda. Make sure to observe what's happening inside the soda as the liquid reacts with the candies. The balloon should be inflating, even if the change is only very slight.

How Does It Work?

The secret behind the famous “popping” of Pop Rocks candy is pressurized carbon dioxide gas. Each of the tiny little candy pebbles contains a small amount of the gas. These tiny carbon dioxide bubbles make the popping sound you hear when they burst free from their candy shells. Need more proof? Try finding a relatively large Pop Rock and using a spoon to break it against a hard surface. Once you achieve enough pressure, you should hear a similar “pop” to the sound you hear with a Pop Rock on your tongue.

So what causes the balloon to inflate? The carbon dioxide contained in the candy isn't enough to cause even the small amount of inflation you observe in the experiment. That's where the soda comes into play. The soda also contains pressurized carbon dioxide gas (it's why we call soda a carbonated beverage). When the Pop Rocks are dropped into the soda, some carbon dioxide is able to escape from the high fructose corn syrup of the soda and, because the carbon dioxide gas has no where to go in the bottle, it rises into the balloon.

Science Fair Connection:

Want to make the Pop Rocks Expander into a science fair project? That's a fantastic idea! There are a number of different variables that you can choose to get that blue ribbon. Remember though, whatever variable you choose, you need to keep everything else the same.

  • Test whether the temperature of soda makes a difference in the amount of carbon dioxide released.
  • Try testing different types (or brands) of soda to see which releases the most carbon dioxide gas.
  • Test different Pop Rocks flavors to see if the flavor changes the amount of carbon dioxide in the balloon.

Those are just a few of the possible variables that you could use, but you're super creative…try coming up with your own!

Additional Info

How are Pop Rocks Made?

According to information from the manufacturer, Pop Rocks start like any other hard candy by combining sugar, lactose (milk sugar), corn syrup, and flavoring. These ingredients are heated to the boiling point and the hot sugar mixture is mixed with carbon dioxide gas under high pressure (about 600 pounds per square inch). The process causes tiny high pressure bubbles of carbon dioxide gas to form in the candy.

When the hot candy mixture cools and the pressure of the gas is released, the hard candy shatters into tiny pieces of carbonated candy. If you look carefully at the candy under a magnifying glass, you'll see the tiny bubbles – each containing a small amount of carbon dioxide gas under high pressure (600 PSI). When the candy melts in your mouth, the 600 PSI bubbles of gas are released with a loud popping sound. Very cool!