The Baby Diaper Secret – SICK Science!

If you've changed a diaper, you've uncovered polymers.

If you’ve ever changed a diaper and noticed what looked like tiny crystals on the baby’s skin, you’ve uncovered the secret of superabsorbent, 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 polymer changed the way parents care for their babies, and scientists continue to find new uses for these superabsorbent polymers.

Experiment Materials

Experiment Videos



Place a new (unused is your first choice) diaper on the piece of newspaper. 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 remove 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 check out the dry polymer you just extracted from the diaper.


Pour the polymer into a plastic cup and 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. You just discovered something that has both a cool and a yuck factor!

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 in 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 (then again, don’t . . . that’s gross).
The cotton-like fibers you removed from the diaper help to spread out both the polymer and the, uh, “water” so that the baby doesn’t have to sit on a mushy lump of water-filled gel. This explanation is getting grosser and grosser! It’s easy to see that even a little bit of polymer powder will hold a huge quantity of water, but it does have its limits. At some point, the baby will certainly let you know that the gel is full and it’s time for new undies!
In spite of their usefulness, these diapers can be a problem. If you’ve ever observed a baby in diapers splashing in a wading pool, you know that even one diaper can absorb lots and lots of water. Most public pools won’t allow them 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 unless you’re a plumber. 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 the cup and smush them down with your fingers. Add a teaspoon of salt, stir it with a spoon, and watch what happens. Salt messes up the gel’s water-holding abilities. When you’re finished, pour the saltwater goo down the drain.
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 little at a time, until it will hold no more. Keep track of how much water the diaper can absorb before it reaches its limit.


Today, superabsorbent polymers are widely used in such applications as 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.