The easiest way to make a foam explosion is the classic “elephant toothpaste” reaction: hydrogen peroxide mixed with a catalyst and dish soap. The catalyst breaks hydrogen peroxide into water and oxygen gas, and the soap traps that oxygen into a rapidly expanding column of foam. You can scale this from a gentle tabletop demo with drugstore supplies to a massive eruption using stronger concentrations.
What Makes the Foam Explode
Hydrogen peroxide naturally breaks down into water and oxygen gas, but on its own this happens extremely slowly. A catalyst speeds up that breakdown dramatically, releasing a huge volume of oxygen all at once. Dish soap catches the escaping gas in thin liquid films called lamellae, which stack up into a dense, stable foam. The more surfactant molecules available, the more of these tiny gas-trapping films can form, which is why a good squirt of soap produces a bigger, thicker foam column than a few drops.
The reaction itself is exothermic, meaning it releases heat. With higher concentrations of hydrogen peroxide, the foam comes out noticeably warm or even steaming hot.
The Beginner Version (3% Hydrogen Peroxide)
This version uses the brown-bottle hydrogen peroxide you already have in your bathroom cabinet. It produces a slow, oozing foam that’s safe for kids to touch.
- Hydrogen peroxide: about half a cup (120 mL) of 3% solution
- Yeast: one packet of active dry yeast dissolved in 3 tablespoons of warm water
- Dish soap: a generous squirt (roughly a tablespoon)
- Food coloring: optional, a few drops for effect
- Container: a tall, narrow bottle or empty soda bottle works best
Pour the hydrogen peroxide into the bottle, add dish soap and food coloring, then pour in the yeast mixture. The foam will rise over the lip of the bottle within seconds. It’s gentle enough that you can pick it up and squeeze it. The yeast works here because it contains an enzyme called catalase, which is extraordinarily efficient at splitting hydrogen peroxide apart. Catalase enzymes can accelerate the reaction by a factor of over 200 billion compared to the uncatalyzed breakdown.
Why Yeast Works So Well
Baker’s yeast naturally produces catalase to protect itself from hydrogen peroxide, which is toxic to cells. When you dump yeast into peroxide, the enzyme goes to work immediately, converting peroxide into water and oxygen gas. The yeast doesn’t get used up in the process, so even a small packet can keep the reaction going until the peroxide runs out. Warm water activates the yeast faster, so dissolving it in water that’s about bath temperature (not hot) gives you a quicker eruption.
The Big Version (30% Hydrogen Peroxide)
This is the version you see in viral videos with foam shooting several feet into the air. It requires 30% hydrogen peroxide, sometimes labeled “beauty grade” or “food grade,” available from beauty supply stores or online chemical suppliers. The higher concentration means far more oxygen is released far more quickly.
- Hydrogen peroxide: 50 to 100 mL of 30% solution
- Catalyst: about 10 mL of saturated potassium iodide solution, or a packet of yeast dissolved in warm water
- Dish soap: a tablespoon or two
- Food coloring: optional
- Container: a large flask, tall vase, or plastic bottle
Potassium iodide produces a faster, more violent eruption than yeast because it triggers the decomposition almost instantly. You dissolve as much potassium iodide as possible into a small amount of water (a saturated solution), then pour it into the peroxide and soap mixture. The result is a sudden, dramatic column of hot foam. With yeast, you get a slightly slower but still impressive eruption since the enzyme takes a moment to ramp up.
For the most dramatic effect, use a container with a narrow neck. The narrow opening compresses the foam and forces it upward like a cannon. Stripe food coloring down the inside walls of the container before adding anything else, and you’ll get a swirled, multicolored column.
Safety at Different Concentrations
The 3% version is essentially harmless. The foam is just soapy water with oxygen bubbles, and you can handle it bare-handed.
The 30% version is a different story. At that concentration, hydrogen peroxide causes chemical burns on contact with skin, producing redness, blistering, and in some cases white patches where the skin has been chemically bleached. It will also damage eyes on contact, potentially causing corneal ulcers. NIOSH classifies solutions above 8% as hazardous materials requiring skin and eye protection. If you’re working with 30% peroxide, wear splash-proof goggles, chemical-resistant gloves, and long sleeves. Do the experiment outdoors or in a well-ventilated space, and keep the bottle of concentrated peroxide capped when you’re not actively pouring.
The foam itself from the 30% version comes out hot. Don’t touch it immediately. After a minute or two it cools, and at that point it’s just soapy water with some residual catalyst.
The Mentos and Soda Alternative
If you want a foam explosion without any chemicals beyond candy and soda, the Mentos-and-Diet-Coke geyser works on a completely different principle. Instead of creating new gas through a chemical reaction, this method releases carbon dioxide that’s already dissolved in the soda.
Each Mentos candy has a rough surface covered in an estimated 50,000 to 300,000 microscopic pits, each about 1 to 3 micrometers across. These tiny imperfections act as nucleation sites, giving dissolved CO2 a place to form bubbles. Drop a few Mentos into a 2-liter bottle of Diet Coke and the rapid bubble formation launches a geyser that can reach several feet. Diet Coke works better than regular because it has lower surface tension, making it easier for bubbles to form and escape.
This version is completely safe to touch (it’s just soda), makes a huge mess, and requires zero preparation beyond opening the bottle and dropping in the candy. The tradeoff is that you get a spray rather than a thick foam column.
Tips for a Bigger Eruption
Several adjustments can increase the size of your foam explosion regardless of which method you choose. Using a taller, narrower container forces the foam upward instead of letting it spread sideways. More dish soap means more lamellae to trap gas, producing denser, longer-lasting foam. Warmer water activates yeast faster, so if you’re using the yeast method, dissolve it in the warmest water you can comfortably touch.
For color effects, you can layer different food colorings around the inside rim of the container so the foam picks up streaks as it rises. Gel food coloring gives more vivid results than liquid drops. Some people add a tablespoon of cornstarch to the soap mixture to thicken the foam and make it hold its shape longer after the eruption.
Cleanup
The foam from the hydrogen peroxide method is mostly water, soap, and dissolved oxygen, so it’s safe to wash down a sink or rinse off pavement with a hose. If you used potassium iodide, the leftover solution can stain surfaces a yellowish brown. Wipe it up promptly and rinse with water. If you used yeast, the residue is just bread yeast and soapy water. For the Mentos version, you’re cleaning up sticky soda, so an outdoor location saves you significant effort.