If you find yourself scratching your head with the latest slime obsession, keep in mind that making slime is actually science! Slime is chemistry! Polymers and non-Newtonian fluids can be a little confusing for young kids, but our short lesson in the science of slime below is a perfect way to answer the question, is slime a solid or liquid? We LOVE homemade slime!

Making Slime With Kids

Making and playing with slime has proven highly fascinating for kids and adults of all ages, but you might not be familiar with basic slime science. Have curious kids who want to know why slime is liquid and a solid?

Basic slime science is great to share with kids who love slime because it’s an excellent learning opportunity already built into an enjoyable hands-on activity.

First, have you ever made an excellent homemade slime with your kids? If you haven’t (or even if you have), check out our collection of the BEST HOMEMADE SLIME RECIPES. Several slime recipes are the foundation for all our slime variations.

The following slime video uses our very popular saline solution slime recipe. Make sure to check out more slime recipe videos.

What Is Slime?

Slime science starts with the best slime ingredients, including the right kind of glue and the right slime activators. You can see all our recommended slime making supplies here.

The best glue is a PVA (polyvinyl-acetate) washable school glue.

You have several slime activators (all in the boron family). These include:

  • saline solution
  • liquid starch
  • borax powder

These slime ingredients or slime activators all contain similar chemicals for making a slime substance. Cross-linking is what happens when the glue and activator are combined!


slime ingredients

Is Slime A Liquid Or A Solid?

Slime involves chemistry!  Chemistry is all about states of matter, including liquids, solids, and gases. It is all about how different materials are put together and made up of atoms and molecules. Additionally, chemistry is how these materials act under different conditions.

Slime is a non-Newtonian fluid. A non-Newtonian fluid is neither liquid nor a solid. It can be picked up like a solid but also ooze like a liquid. 

Our 2 ingredient oobleck is another example of a non-Newtonian fluid!

You will notice that slime has no specific shape and will change it to fill whatever container it’s placed in.  However, it can also be bounced like a ball because of its elasticity.


Slime is an example of Shear-thickening fluids or fluids in which stress causes an increase in viscosity. When shear stress, such as quickly stirring or pulling the slime apart, the slime shears or breaks. Pull the slime slowly, and it flows more freely. If you pull it quickly, the slime will break off more easily because you break apart the chemical bonds.

What Makes Slime Stretchy?

Slime is all about polymers! A polymer is made up of very large chains of molecules. The glue used in slime comprises long chains of polyvinyl acetate molecules (that’s why we recommend PVA glue). These chains slide past one another fairly easily, that keeps the glue flowing.

Chemical bonds are formed when you mix the PVA glue and slime activator together.  Slime activators (borax, saline solution, or liquid starch) change the position of the molecules in the glue in a process called cross-linking!  A chemical reaction occurs between the glue and the borate ions, and slime forms the new substance.

Instead of flowing freely as before, the molecules in the slime have become tangled and create what is slime. Think wet, freshly cooked spaghetti versus leftover cooked spaghetti! Cross-linking changes the viscosity or flow of the new substance.

Slime Science Project

You can experiment with the viscosity or thickness of slime using our basic slime recipes. Can you change the viscosity of slime with the amount of slime activator you use? We show you how to set up your own slime science experiments in the link below.


slime science

Can You Make Slime Without Borax?

Concerned that borax is not good for you?  We have several taste-safe borax-free slime recipes for you to try.  Find out what fun substitutes for borax you can make slime with! Please note that a borax-free slime will not have the same texture or stretch as traditional slime.


Borax Free Slime

Slime Recipes To Try

We also have the most popular recipes kids want to be making right now, like crunchy slime, butter slime, and cloud slime (to name a few)!

Click on the photos below to see all the kinds of slimy resources available. Get our ultimate slime-making pack to download and print!

Grab the Ultimate Slime Recipe Bundle

All the best homemade slime recipes in one place with plenty of fantastic extras! Plus, it includes a slime science guide!

Includes a Slime Science Project Pack!

  • The Ultimate Slime Guide contains all the specialty recipes you or your kids want to make! You’ll find all the best tips, tricks, hints, and slime-y info in almost 100 pages!
  • The Ultimate Slime Holiday Guide covers all the best holidays and seasons with special themes and slime-y projects!
  • The Ultimate Borax-FREE and Taste-Safe Slime Guide shows you how to make all the best borax-free, taste-safe, and non-toxic slimes kids love, such as marshmallow slime. These recipes do not use chemical activators such as saline solution, liquid starch, or borax powder, making them truly borax-free.
  • The Ultimate Slime Coloring Book is an easy-to-print coloring book kids will love! Color and design your favorite slimes!
  • The Slime Starter Guide is a fact-filled information guide with everything you need to know to make the best slime ever!
  • Slime Science Project Pack helps you turn slime-making into a science lesson!


  1. For your information, Slime is created when PVA, in other words Polyvinyl acetate, comes in contact with sodium borate, sodium tetraborate, or disodium tetraborate. Slime is a very easy craft that me and my class love so much, that we make it every Monday! We recommend the following slimes: Floam slime, Fluffy slime, Iceburg slime, Crystal clear slime, and Bubble Rap slime.

  2. We use the box of McCormick liquid food coloring bottles from the spices section of the grocery store!

  3. HI,
    I’m concerned that borax is not good for you. Does the borax react with the PVA to make it less dangerous?

  4. Have you checked out Steve Spangler? He has a great video or two on Facebook regarding the safety of borax powder for slime making.

  5. there are two different types of borax. one is detergent, and one is to kill insects. the detergent is safe, but NOT the killer one

  6. Actually boric acid which is in the same boron family as borax powder is what is used in insecticides as well as eye drops. Borax powder is laundry, some hand soaps and trace in fertilizer since it is mined through the ground. Through an intense processing borax powder can be turned into boric acid. They are however, not exactly the same.

  7. tried different versions of your recipes, with the saline solution we had at home, and the result is too liquid every time… do all saline solutions contain sodium borate? the label on my saline solution does not mention it, therefore I wonder if that isn’t the reason why it doesn’t work. is there something else I can use instead? i was hoping to avoid borax

  8. Yes, your saline needs the ingredients boric acid and sodium borate to work properly. Depending on your location, you can also try liquid starch.

  9. slime is amazing you can do anything with it like: Put it in stress balls, or play with it with your hands. Also, it’s a great stress reliever I do recommend this. Thx for the recipes 😀

  10. Hi there- I want to use your liquid starch slime recipe for my first grade Halloween party–Can you tell me if one recipe is for one kid or for how many—so for a class of 24- do I make 24 recipes?


  11. Hi! One recipe will make quite a bit of slime. One batch could easily be split 3-5 ways depending on how much you want each kid to end up having. I like the condiment size containers that hold about 2oz each! One batch usually fills about 5 of those! Feel free to email me [email protected] if you would like to talk about it more!

  12. As someone who’s read about and experienced PVA and borax together I would say that you should probably stay away from it. I know that there were many reports on the news about kids getting burns from the borax in their slime. Personally I did not get burned but my hands did feel tingly and slightly hot. All in all it does work as an activator but I would advise to choose another activator like detergent or contact lenses solution.

  13. Sensitivity is a huge issue. However, my skin did not like laundry detergent at all and I highly advise to stay away from laundry detergent which is why we do not have a recipe for it. We use less borax than most recipes, and if you do have sensitive skin I would choose saline solution (not contact lens solution). Liquid starch is another choice. All the choices contain some form of borons.

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