How to Make Slime? The Fun and Fascinating Science Behind Making Your Own Slime

How to Make Slime? The Fun and Fascinating Science Behind Making Your Own Slime

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Slime is among the most popular toys and DIY projects, especially among kids and teens. Playing with slime is fun, soothing, and addictive. The best part is that you can easily make slime using just a few ingredients at home.
In this guide, you’ll learn everything about making slime, from its science to step-by-step instructions for making different types of slime. Read on to become a slime-making expert!

What is Slime?

Slime is a thick, sticky, stretchy substance with a rubbery texture. It is made by cross-linking polymers – long chains of molecules that create a 3D network when they interact.

The most common ingredients used to make slime are:

  • Glue – Provides polymers (long chains of molecules) to create the stretchy slime texture. Elmer’s white glue or clear glue is most commonly used.
  • Borax or Liquid Starch – The cross-linking agent that binds the polymers together to create the unique properties of slime.
  • Water – Activates the cross-linking agent and adjusts the slime consistency.
  • Food colouring, glitter or other add-ins – For decorative slime varieties.

When borax or starch is mixed into the glue solution, the polymers become “cross-linked,” creating a 3-dimensional network that gives the slime stretch and ooziness. Adding activators like baking soda can strengthen these cross-links further.

The Fascinating Science of Slime

Slime is an example of a “non-Newtonian fluid.” This means its viscosity (how easily it flows) changes based on the amount of force applied.
At rest, the polymers are loosely linked together, so the slime remains thick and gooey. But when you slowly pull on it, the polymers align, and the slime stretches. When stress is removed, the polymers slide past each other, and the slime oozes back to its original shape.
Unlike Newtonian fluids like water, whose viscosity stays constant, slime alters viscosity based on external forces. This property makes playing with slime so unique and fun!
Slime also exhibits properties like viscoelasticity – it can both flow like a liquid and deform/bounce back like a solid. Understanding non-Newtonian fluids like slime helps scientists develop real-world applications from medical devices to body armour.

Borax vs Baking Soda – The Secret to Great Slime

The key to making tremendous slime is using the right cross-linking agent. The most common options are borax powder or baking soda.


Borax, aka. Sodium borate is a natural mineral salt that acts as an excellent cross-linker to create slime. When borax is mixed with glue, it forms bonds between the polymer chains, turning the glue into a stretchy, putty-like slime.

  • Creates thick, glossy slime with excellent stretchiness
  • It is more accessible to incorporate add-ins like foam beads or glitter


  • It can take a few hours to fully set after mixing
  • The resulting slime has a stickier, tackier texture

Baking Soda

Baking soda, aka. Sodium bicarbonate can also be used to make slime. It reacts similarly to borax by binding to the glue polymers.

  • Sets faster, usually 5-10 minutes after mixing
  • Produces a smoother, less sticky slime


  • It can be more challenging to mix thoroughly, resulting in pockets of unreacted glue
  • Slime has less stretch and glossiness than borax slime

For super stretchy, thick, bubbly slime, borax is the better choice. For fast-setting slime that has a smoother texture, baking soda works well. Just be sure to mix thoroughly when using baking soda to avoid any powdery bits left over.

Slime Making Basics

Now that you know the science behind slime, let’s review the primary method and ingredients to whip up your slime!
Supplies Needed:

  • Glue – white school glue or clear glue. For extra-stretchy slime, use clear glue.
  • Activator – Borax powder or baking soda
  • Water
  • Plastic bowl & spoon for mixing
  • Food colouring, glitter, or other mix-ins (optional)

Basic Slime Recipe:

  1. Pour 1 cup of glue into a container.
  2. Mix 1 teaspoon of borax powder and 1 cup of warm water in a different bowl until fully dissolved. This is your slime activator solution.
  3. Add in food colouring if desired. 2-3 drops yield vibrant color.
  4. Slowly mix the activator solution into the glue, 1 tablespoon at a time. Mix thoroughly after each addition.
  5. Once thoroughly combined, knead the slime with your hands until it reaches the desired stretchiness and consistency.
  6. Store all slime in an airtight container to prevent drying out.

Tips for Making Perfect Slime:

  • Use room temperature or slightly warm water to aid in the dissolving of borax
  • Mix in the activator slowly to prevent clumping
  • Knead the slime well once mixed to activate the cross-linking
  • If the slime is too sticky, add a teaspoon more borax solution
  • For thicker slime, allow it to sit 1-2 hours after mixing to fully set
  • To thin out slime, work in a little extra glue
  • Store slime in an airtight container or ziplock bag to prevent drying out

Fun Slime Add-Ins and Variations

Once you master the basic slime recipe, you can get creative with fun add-ins to make Insta-worthy slimes! Here are some cool variation ideas:

  • Glitter slime: Add 1-2 teaspoons of fine glitter and mix thoroughly. Creates a sparkly, shimmery slime.
  • Foam bead slime – Mix in 1-2 tablespoons of coloured foam beads. Results in a fluffy slime stuffed with beads.
  • Dye slime: Use liquid food dye, neon pigments, mica powder, or eye shadow to create vibrant coloured slimes.
  • Scented slime: For refreshing scented slime, add a few drops of scented essential oils like peppermint, lavender, orange or lemon.
  • Crunchy slime – Mix in 1 tablespoon of cornstarch to give your slime a satisfying crunch.
  • Glow in the dark slime: Use glow powder to make slime that lights up in the dark! Charge it under a lamp beforehand.
  • Fluffy slime: Whip slime mixture with a hand mixer during preparation to incorporate tiny air bubbles. Results in a fluffy, cloud-like slime texture.

Clear glue slime: Use clear glue as the base for see-through varieties. Add clay, beads, charms, or foam shapes for even more texture. The possibilities are endless when you get creative with slime!

Storing Slime Correctly

Slime is perishable and can dry out if not stored properly. Follow these tips to help your slime last longer:

  • Store slime in an airtight container like a plastic jar or ziplock bag. Squeeze out excess air before sealing.
    If storing multiple slime varieties together, place them in separate containers or bags to prevent colours from bleeding and mixing.
  • Keep slime away from direct heat or sunlight, which can cause drying.
  • Re-wet slime with a few drops of water or glue if it starts to dry and lose stretchiness. Knead to reactivate.
  • Slime lasts 1-3 months if stored airtight in a cool, dark place. Refrigeration can prolong shelf life.
  • If slime becomes too sticky and tacky, work in a little extra borax solution to re-set it.

With the proper storage, you can keep your slime in optimal play-ready condition for months of stretching and squishing!

Safety Tips for Making & Playing with Slime

While slime-making is fun for all ages, there are a few precautions to take for safety:

  • Supervise young children closely and avoid small objects that could pose a choking hazard if accidentally mixed into slime.
  • Borax can be irritating to the skin and eyes. Wear gloves during preparation and wash hands after handling borax mixtures.
  • Store slime out of reach of pets who may try to taste it. Ensure all ingredients are non-toxic.
  • Avoid getting slime stuck in your hair or on furniture/clothes. Apply a little oil to remove slime from surfaces.
  • Do not eat slime! While borax is low-toxicity, slime should be considered a play material rather than food.

With adult supervision and by following basic safety guidelines, enjoying slime is educational and creatively stimulating for all ages!

FAQs About Slime

Now that you’re a slime expert in the making, here are answers to some frequently asked slime questions:

Why is my slime sticky/stringy?

  • Not enough activator – Stickiness usually means the slime needs more borax or baking soda to fully cross-link the polymers. Work in a more activator solution.
  • Old or expired glue – Glue can lose efficacy over time. Old or expired glue may not react as well to form good slime. Use fresh school or craft glue.
  • Too much activator – Conversely, too much borax can make the slime sticky. Add a teaspoon of glue to balance it out.
  • The environment is humid/damp – Absorbing moisture from the air can make slime sticky. Store it sealed in an airtight container.
  • Not kneaded enough after mixing – Knead the slime vigorously once mixed to fully incorporate the activator and polymers.
  • Dried out – If slime is exposed to air and dries out, it will become tacky. Re-wet with a bit of water or glue and knead to restore elasticity.

You can achieve the perfect slime texture with the correct ingredient ratio and kneading technique. Adjust the recipe as needed if your slime turns too sticky or stringy.

Tips and information about making slime to address stickiness and stringiness:

  • Use clear glue for less stickiness – Clear glues like Elmer’s contain fewer impurities than white school glue. The result is clearer, less sticky slime.
  • Add lotion, glycerin, or liquid starch – These can lubricate the slime and make it less tacky. Add 1-2 teaspoons and mix well.
  • Avoid over-activating – Adding too much borax can make slime stiff and stringy. Mix in more glue to rebalance.
  • Knead with oil on hands – Coating hands in a thin layer of oil like baby oil or coconut oil while kneading helps prevent slime from sticking.
  • Adjust temperatureSlime made and stored at cooler temps may turn more sticky. Try making slime at room temperature.
  • Let it rest – Stickiness can improve after giving freshly made slime for 1-2 days, sealed in an airtight container to fully cure.
  • Check ingredients – Ensure borax/baking soda is fresh and fully dissolved. Use warm water and mix the activator well before adding.
  • Humidity and drying – These are the biggest causes of stickiness. Store slime properly sealed and away from excess moisture or dry air.

With practice, you’ll get a feel for making the perfect consistency slime – stretchy and bubbly without overly sticky or stringy. Keep trying if your first few batches turn out. Slime-making is fun, creative science!

Some other common mistakes to avoid when making slime:

  • Not mixing the activator properly: The borax or baking soda solution needs to dissolve fully before mixing into the glue. Make sure no powder bits remain.
  • Poor quality glue: Cheap “school glues” often contain more impurities than craft glues like Elmer’s. This can make slime turn out stringy. Invest in better glue.
  • Adding activator too quickly: Mix the borax/baking soda solution in slowly and a little at a time to prevent clumping. Go slowly.
  • Not kneading thoroughly: Take the time to knead the mixed slime for a few minutes to activate the cross-linking reaction. This makes slime stretchier.
  • Using distilled water: Tap or bottled water works better. Distilled water prevents the borax from dissolving and reacting correctly.
  • Adding too many extras: Going overboard on glitter, beads, or foam can prevent the slime from setting up properly. Add sparingly.
  • Letting slime freeze: Slime turns more stringy and sticky if frozen, so don’t store it in freezing temperatures. Keep at room temp.
  • Microwaving slime: Heat can break down the bonds in slime. Never microwave slime to try and re-liquefy it.

With practice and avoiding these errors, you can create perfect picture-worthy slime every time!

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