Oobleck Slime Recipe: Easy 2-Ingredient Guide

Oobleck is a classic two-ingredient slime that behaves like both a liquid and a solid, depending on how you handle it. It’s a non-Newtonian fluid, meaning it flows when poured slowly but turns firm when squeezed or struck. This simple cornstarch-and-water mixture is a favorite for sensory play and science demonstrations, and it takes just minutes to make with pantry staples.

What You’ll Need

1 cup (128 g) cornstarch (also called cornflour in the UK)
½ cup (120 ml) water, plus more as needed
Food coloring (optional, a few drops)
Large mixing bowl
Spoon or spatula for stirring
Measuring cups

Step-by-Step

Measure the cornstarch. Add 1 cup (128 g) of cornstarch to your mixing bowl. If you want colored oobleck, mix a few drops of food coloring into the water before adding it.
Add the water. Pour ½ cup (120 ml) of water into the bowl with the cornstarch. Do not dump it all in at once; a slow pour helps avoid lumps.
Stir slowly. Use a spoon or spatula to mix the cornstarch and water together. Stir gently at first—the mixture will feel stiff and difficult to move. That’s normal.
Check the consistency. Once the mixture is combined, it should look like a thick liquid when you stop stirring. If it’s too dry and crumbly, add water one tablespoon (15 ml) at a time until it flows slowly when tilted.
Test the oobleck. Quickly punch or squeeze a handful of the mixture. It should feel solid and resist your grip. Then, open your hand and let it drip—it should flow like a liquid. If it doesn’t do both, adjust the ratio: add a pinch more cornstarch if it’s too runny, or a splash more water if it’s too stiff.
Play and explore. Use your hands to scoop, roll, and let it ooze. You can also place it in a shallow tray and tap the surface to see it crack. When you’re done, store it in an airtight container.

Common Mistakes

Adding too much water at once. This makes the oobleck too runny and soupy. Always add water gradually.
Stirring too vigorously. Fast stirring makes the mixture seize up and feel like a solid, which can be frustrating. Stir slowly and gently.
Using warm water. Warm water can make the cornstarch clump more easily. Use cool or room-temperature water for a smoother mix.
Expecting it to stay solid. Oobleck is not like traditional slime; it will always return to a liquid state when left alone. That’s the point.

Tips

Use a ratio of 2:1. The classic ratio is 2 parts cornstarch to 1 part water by volume. Start there and adjust slightly if needed.
Add glitter or sequins. Mix in a teaspoon of fine glitter for extra sparkle without changing the texture much.
Make it glow. Use tonic water (which contains quinine) instead of regular water, then shine a black light on the oobleck for a glowing effect.
Clean up with warm water. Oobleck dries to a powder, so wipe surfaces with a damp cloth and wash hands with warm soapy water.
Store properly. Keep it in a sealed container or zip-top bag. It will last for a few days, but it may need a splash of water to refresh it.

Troubleshooting

It’s too runny. Add more cornstarch, a tablespoon (8 g) at a time, and stir gently until it thickens.
It’s too stiff and crumbly. Add water a teaspoon (5 ml) at a time until it comes together into a smooth, flowing mass.
It’s full of lumps. Let the mixture sit for 2–3 minutes, then stir slowly. The lumps usually dissolve on their own.
It dries out during play. Sprinkle a little water over the surface and knead it in. Oobleck dries quickly, so keep a small bowl of water nearby.
It’s sticking to your hands. That’s normal—just rinse with water. Avoid using soap until after you’ve rinsed off the bulk of the cornstarch.

Frequently Asked Questions

Why is my oobleck not solid when I punch it?

If it doesn’t firm up when squeezed, the ratio is off. Add more cornstarch a little at a time until it reaches the right consistency. It should feel like a wet sand that holds its shape under pressure.

Can I use flour instead of cornstarch?

No, flour will not produce the same non-Newtonian effect. Cornstarch is essential because its fine, powdery particles create the unique liquid-solid behavior. Flour makes a sticky paste instead.

Is oobleck edible?

It’s not toxic, but it’s not meant to be eaten. The taste is unpleasant, and eating large amounts could cause stomach upset. For very young children who mouth everything, use a taste-safe version with cornstarch and water only, and supervise closely.

How long does oobleck last?

In an airtight container, oobleck can last for 2–3 days at room temperature. After that, mold may start to grow. You can refrigerate it to extend its life slightly, but it’s best to make fresh batches for each play session.

Can I make oobleck without measuring cups?

Yes, you can eyeball it. Use a handful of cornstarch and add water slowly until you get the right texture. The key is to add water gradually and test as you go.

What do I do with oobleck after playing?

You can compost it or throw it in the trash. Do not pour it down the drain—the cornstarch can clog pipes. Wipe up any residue with a dry paper towel before washing surfaces.

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Safety notes: safe minimum internal temperatures from USDA FSIS; raw and undercooked fish guidance from the U.S. FDA. Food safety notes

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