The Baby Diaper Secret – Science Experiment

If you've changed a diaper, you've witnessed the magic of polymers.

The Baby Diaper Secret: A Lesson in Super-Absorbent Polymers

How do diapers work? Well, if you’ve ever changed a baby diaper, you’ve witnessed the magic of polymers. Learn how polymer crystals work in baby diapers and get a firsthand view of superabsorbent polymers and a super-cool lesson about how they affect the absorbency of diapers!

Clear Crystals in Baby Diapers: What are They?

Have you ever changed a diaper and noticed what looked like tiny clear crystals on the baby’s skin? If so, then you’ve uncovered the secret of disposable diapers. Those tiny crystals actually come from the lining of the diaper and are made out of a safe, nontoxic polymer that absorbs moisture away from the baby’s skin. This amazing superabsorbent polymer material changed the way parents care for their babies. Scientists are still learning about these amazing substances and are finding new uses for these superabsorbent polymers. If you’ve ever wondered what diapers materials are made of, then this science experiment is for you!

SICK Science® is a registered trademark of Steve Spangler, Inc. All Rights Reserved.

Experiment Materials

Experiment Videos



Place a new and unused disposable diaper on the piece of paper. Carefully cut through the inside lining and remove all the cotton-like material. Put all the stuffing material into a clean, zipper-lock bag.


Scoop up any of the polymer powder that may have spilled onto the paper and pour it into the bag with the stuffing. Blow a little air into the bag to make it puff up like a pillow, then seal the bag.


Shake the bag for a few minutes to separate the powdery polymer from the stuffing. Notice how much (or how little) powder falls to the bottom of the bag.


Carefully remove the stuffing from the bag and pour the dry polymer you just extracted from the diaper into a small, clear cup.


Fill the cup with about 4 ounces (120 mL) of water. Mix it with your finger until the mixture begins to thicken.


Observe the gel that the polymer and water create. Turn the cup upside down and see how it has solidified. Now you know the super, moisture-absorbing secret hiding in the lining of a baby diaper.

How Does It Work

The secret, water-absorbing chemical in a diaper is a superabsorbent polymer called sodium polyacrylate. A polymer is simply a long chain of repeating molecules. If the prefix “poly” means many, then a polymer is a long chain of molecules made up of many smaller units, called monomers, which are joined together. Some polymers are made up of millions of monomers. Superabsorbent polymers expand tremendously when they come into contact with water because water is drawn into (and held by) the molecules of the polymer. They act like giant sponges: some can soak up as much as 800 times their weight in water. Just imagine how much water a giant diaper could hold!

The cotton-like fibers you removed from the baby diaper help to spread out both the polymer and the liquid so that the baby doesn’t have to sit on a mushy lump of water-filled gel. It’s easy to see that even a little bit of polymer powder will hold a huge quantity of water. It does, however, have its limits.

Despite their usefulness, these diapers can be a problem. If you’ve ever observed a baby in a diaper splashing in a wading pool, you know that even one diaper can absorb lots and lots of water. Most public pools won’t allow baby diapers to be worn in the water because huge globs of gooey gel can leak out and make a mess of the filter system. Also, some folks used to throw them away in toilets — not a good idea! For the most part, however, these diapers are a great invention and make for dry, happy babies.

Take It Further

Put the pieces of gel back into a cup and smush them down with your fingers. Add a teaspoon of salt and stir it with a spoon. Then, watch what happens. Salt messes up the gel’s water-holding abilities. When you’re finished, pour the saltwater goo down the drain.

Science Fair Connection

While adding water to a super water-absorbing polymer and watching it solidify is fascinating, it is not a science fair project — yet. You can create a polymer-themed science fair project by identifying a variable, or something that you can change, in an experiment. Let’s take a look at some of the variable options of these water-absorbent materials that might work.

  • Try testing for the baby diaper with the fastest reaction by using different temperatures of water. Which temperature of water creates the fastest reaction?
  • Test different brands of diapers to find the different absorbency of diapers. Be sure to use the same size baby diaper even though you are testing different brands. If you test a toddler-sized diaper against a newborn-sized diaper, your results will not be reliable. Keep everything the same except for the brand of baby diaper being tested. For each brand, grab a new diaper and slowly pour about 1/2 cup of warm tap water into the center. Hold the diaper over a large pan or sink and continue to add water, a small amount at a time, until it will hold no more. Which baby diaper has the most super absorbent polymer? Which of those gels absorb water the quickest? The brand of diaper is the variable in this experiment. You’ll find out quickly if you get what you pay for or if there really isn’t much of a difference between different brands of diapers. What are the most absorbent diapers? New moms will be very interested in the findings of this experiment!

These are just a couple of ideas, but you aren’t limited to them! Come up with different ideas of variables to test and give them a try. Remember, you can only change one variable at a time for each test. For example, if you are testing different water temperatures to find the most absorbent diapers, make sure that all other factors in the test remain the same! These diaper materials are amazing, and you’ll find new ways to experiment with the absorbency of diapers that will be an interesting and engaging science project experiment.


Superabsorbent polymers aren’t just used in different brands of baby diapers. Today, these water-absorbent materials are widely used in many applications like forestry, gardening and landscaping as a means of conserving water. Imagine using a substance that could store water in the soil and then release it as the plants’ roots needed it. While we may consider water-absorbing polymers to be a modern convenience, the impact that such technology is having on parts of the world that are plagued by drought is remarkable.

Superabsorbent Polymer Materials and More

If you had fun learning how polymer crystals work in baby diapers, then you’ll have a blast with our other online science experiments! From the clear crystals in baby diapers to chemistry experiments, biology and earth science, you’ll find a great range of different online experiments for kids here at Steve Spangler Science. Shop all-in-one science STEM kits, lab supplies and other hands-on products that are fun for kids of all ages. Have fun, explore the world around you and keep asking questions!

Retail Ad – 20200316
Club Ad – 20200316

Related Products