The Science of Slime: What makes Slime work?

Slime is more than just a squishy, stretchy toy—it’s a hands-on science experiment that you can do at home! Whether you’re stretching it, pulling it, or watching it ooze through your fingers, there’s a fascinating world of chemistry at work behind the scenes.

From the simple glue-and-borax mixture that creates the standard slime we all know, to the airy, pillow-soft texture of fluffy slime, and even the strange, shape-shifting properties of non-Newtonian Oobleck, each type of slime offers a fun way to explore scientific concepts like polymers, chemical reactions, and fluid dynamics.

Discover how the ingredients in different slime recipes combine to create new materials with surprising properties. Let’s explore the science behind slime.

Basic Slime Recipe Chemistry

The classic slime recipe is made from just a few simple ingredients: white glue, water, and borax (or a saline solution containing borate). When we mix these ingredients together, we get a stretchy, squishy substance that we know as slime. This type of slime is easy to make and has become a staple of DIY science projects because of the simple chemistry behind it.

You can add coloring (we added some green food coloring in the above photo), glitter, or plastic decorations for variations on the theme or seasonal slime, but the recipe is pretty universal:

Key Ingredients:

• Glue: Typically, white school glue is used, which contains a polymer called polyvinyl acetate (PVA).
• Borax or Saline Solution: Borax powder dissolved in water or a saline solution that contains borate ions.
• Water: Added to adjust the consistency of the slime and help with mixing.

The Science of Cross-Linking

What makes the glue turn squishy and stretchy? The science behind slime lies in a process called cross-linking. The main ingredient in glue, polyvinyl acetate (PVA), is a polymer, which means it’s made up of long chains of repeating molecules (called monomers) that are all tangled together, forming chemical bonds. On its own, PVA behaves like a thick liquid because these chains can slide past each other.

When borax (or borate from saline solution) is added to the glue, the borate ions start to form bonds between the polymer chains. These bonds are called cross-links, and they act like little bridges that connect the chains together.

Once the polymer chains are connected, they can no longer slide past each other as easily. The glue thickens to the texture we know as slime!

Properties of Standard Slime

The fun part of slime is its elasticity (stretchiness) and viscosity (resistance to flow), both of which are controlled by how much cross-linking occurs between the polymer chains.

The more borax you add, the more cross-links are formed, making the slime stiffer and less stretchy. With just the right balance, you get the perfect slime that’s stretchy, squishy, and fun to play with.

Fluffy Slime: Chemistry Meets Foam

If we add in some different ingredients, we can change the properties of our slime.

What is Fluffy Slime?

Fluffy slime takes the classic slime recipe to a whole new level by adding shaving cream, which gives it a soft, pillowy texture and extra volume.

While it shares the same basic chemistry as standard slime, the addition of foam from the shaving cream introduces air bubbles that physically change the slime’s texture, making it lighter, softer, and fluffier. Fluffy slime feels almost like a marshmallow and is less dense than regular slime, making it a favorite for sensory play.

Key Ingredients:

• Glue: White school glue, which contains polyvinyl acetate (PVA).
• Borax or Saline Solution: Borax dissolved in water or a saline solution containing borate ions, which acts as the cross-linking agent.
• Shaving Cream: This is what makes the slime fluffy by adding foam filled with air bubbles.
• Water: Used to adjust the consistency.

The Science Behind Fluffy Slime

Fluffy slime involves the same basic chemical reaction as standard slime, and makes it “fluffy” with the shaving cream, which is a foam composed of soap, water, and most importantly, air bubbles.

Shaving cream is essentially a mixture of gas (air) trapped inside a liquid, and when mixed with the glue and borax solution, these air bubbles get incorporated into the slime. The cross-linking process still happens between the polymer chains in the glue, but now the slime is full of tiny air pockets. In this case, the slime’s texture is changed more by physical forces (air bubbles) than by chemical ones.

The shaving cream doesn’t chemically react with the glue or borate ions; instead, it simply gets mixed into the slime and introduces extra space (air) within the polymer structure. These trapped air bubbles give the slime a light, airy feel and increase its volume without changing the actual chemical structure of the slime itself. The more shaving cream you add, the fluffier and softer the slime becomes!

Properties of Fluffy Slime

Fluffy slime can stretch and be molded, but it often won’t stretch as far as standard slime because the air pockets in the foam weaken the bonds between the polymer chains. This makes fluffy slime softer and more prone to breaking when stretched quickly, but also gives it that characteristic “fluffy” texture.

Oobleck: The Magic of Non-Newtonian Fluids

Once variation of slime borrows its name from a Dr Seuss Story, Bartholomew and the Oobleck.

What is Oobleck?

Oobleck is a type of slime that behaves very differently from the standard slime recipe or fluffy slime. Made from just cornstarch and water, it has a unique property that allows it to act like both a liquid and a solid, depending on how much pressure or force is applied.

This makes Oobleck an example of a non-Newtonian fluid—a substance that doesn’t follow the normal rules of how liquids behave. Though Oobleck takes its name from a Dr. Seuss book, its behavior is rooted in real science.

Key Ingredients:

• Cornstarch: The main ingredient that gives Oobleck its strange properties.
• Water: The liquid that binds everything together and allows the cornstarch particles to move.

The Science Behind Oobleck

The magic of Oobleck lies in the way it behaves when different amounts of force are applied. Typically, liquids behave according to Newton’s law of viscosity, meaning their thickness (or viscosity) stays the same no matter how much force you apply.

For example, water flows the same whether you pour it slowly or stir it quickly. But oobleck doesn’t follow this rule, which is why it’s called a non-Newtonian fluid.

Oobleck is a shear-thickening fluid, which means its viscosity increases when you apply more force. When you press or hit oobleck hard, the cornstarch particles are forced together, and the mixture behaves like a solid.

But when you handle it gently or let it sit still, the particles are able to move past each other freely, and it flows like a liquid. This unique property is due to the interaction between the cornstarch particles and the water. You can see this dripping effect in the photo above., as the mixture is at rest.

Cornstarch is made of tiny, rigid particles, and when mixed with water, these particles are suspended in the liquid. When you apply force, the water is pushed out from between the cornstarch particles, causing them to jam together and resist movement. This is why oobleck feels solid when you poke or punch it.

However, when the force is removed, the water flows back between the particles, allowing them to move freely again and making Oobleck behave like a liquid.

Properties of Oobleck

Oobleck doesn’t involve any chemical reactions—its behavior is purely a result of the physical interactions between the cornstarch particles and water. This makes it a fantastic demonstration of fluid dynamics and a great way to explore non-Newtonian fluids.

In addition to being a fun hands-on experiment, oobleck can also be used to demonstrate real-world concepts. For example, some types of body armor and athletic gear use non-Newtonian materials that harden under impact to protect the wearer, similar to how oobleck behaves when struck. It’s a simple recipe, but it illustrates some fascinating physics that even scientists use in advanced technologies!

Other Fun Variations of Slime

While standard slime, fluffy slime, and oobleck are some of the most popular and well-known types of slime, there’s an entire world of slime variations out there just waiting to be explored! From glow-in-the-dark slime to magnetic slime, each new recipe brings its own unique texture, color, or special effect, making slime one of the most versatile DIY science experiments around.

Want to make slime that glows after you charge it under a light? How about slime that stretches and pulls towards a magnet? Maybe you’re curious about creating slime themed for Halloween.

The Science in Action: What Kids Can Learn from Slime

Making slime isn’t just a fun and creative activity—it’s also a fantastic way for kids to learn important scientific concepts in a hands-on, engaging way. Every time kids mix up a batch of slime, they’re exploring real science, from the chemistry of polymers to the behavior of non-Newtonian fluids. Slime-making provides an opportunity to explore how different materials interact and change when combined, offering a playful introduction to the world of STEM (science, technology, engineering, and math).

Introduction to Chemistry

• Slime-making teaches kids about polymers, which are long chains of molecules that give materials like glue their flexible, liquid-like properties. By adding borax or a saline solution, kids learn how chemical reactions can change the structure of these polymers, turning them from liquid to solid. This process, known as cross-linking, helps kids understand how molecules connect and interact with each other.
• When kids experiment with different types of slime, like fluffy slime or glow-in-the-dark slime, they’re seeing how slight changes in ingredients can result in big changes in texture, color, and consistency, all thanks to chemistry.

Material Science and Physics

• Slime is also a great way to introduce kids to material science. Whether it’s the stretchy, gooey feel of standard slime or the solid-but-liquid behavior of oobleck, kids can see how materials behave differently depending on their composition and how much force is applied.
• With oobleck, kids dive into the world of fluid dynamics, learning about non-Newtonian fluids and how some substances change their state based on pressure and movement. Watching oobleck harden under pressure and flow like a liquid when left alone is an exciting way to experience real-world physics.

Encouraging Curiosity and Experimentation

• Slime-making encourages kids to experiment and ask questions. What happens when you add more shaving cream to fluffy slime? Can slime stretch even further if you use more glue? By playing with slime, kids naturally engage in scientific thinking—observing, hypothesizing, testing, and drawing conclusions.
• The variety of slime recipes allows kids to explore how small changes in ingredients can lead to different results. It’s a fun and safe way to experiment with cause and effect, sparking curiosity and a deeper understanding of the science behind everyday materials.

Hands-On STEM Learning

• Slime is an ideal tool for hands-on STEM learning. It brings science to life in a tangible, accessible way that’s enjoyable for kids of all ages. Whether they’re making slime for the first time or trying a more complex recipe, kids are developing problem-solving skills, creativity, and a love for discovery that will serve them well in future scientific explorations.

Wrap Up – The Science Behind Slime

Slime may seem like a simple playtime activity, but behind every stretch, squish, and swirl, there’s science at work. Whether you’re using standard slime ingredients like glue and borax, experimenting with the soft, fluffy texture of shaving cream slime, or exploring the unique behavior of oobleck, each recipe offers something different; different texture and different elements of science.

From understanding how polymers link together to observing the strange properties of non-Newtonian fluids, slime-making is a fun and hands-on way to learn some deep concepts.

Slime teaches us about the way materials interact, change, and behave under different conditions, all while offering endless opportunities for creativity and play.

Have fun and try out new recipes. Test different variations, and keep asking questions about why certain ingredients make slime stretchier, fluffier, or more colorful.

Through slime, you’re not only having fun but also diving into the exciting world of science, where discovery is always just a squishy handful away!