Water absorbing crystals can absorb 30 times their weight in water. They are used in gardens or in neckties for athletes to use to keep cool. Also called hydrogels, water crystals are made by mixing three ingredients. The problem is that one of those ingredients is impossible to buy and difficult to make. Instead, use polymer powder found in baby diapers to make crystals.
Place the diaper on the paper so that the inside faces up. Cut through the inside of the diaper with the scissors. Cut a long line or a big strip of the diaper.
Pull out the cotton material that is inside the diaper. Put the material in the freezer bag. Try to get out every bit of the material from inside the diaper. Dump some out onto the paper if necessary. Fold the paper and use the folded middle as a spout to pour more of the material into the bag.
Blow air into the bag and then seal it. It should look like a balloon with cotton inside. Shake the bag for several minutes. The polymer powder will fall from the material and rest at the bottom of the bag. Remove the cotton material from the bag.
Put 1/4 teaspoon of the polymer powder in a bowl. Pour 1 cup of water into the bowl. The powder will absorb the water and become crystal shaped. Let the powder and water sit for at least 1 hour.
Experiment with the amount of water used to make the crystals different sizes. Smaller crystals will absorb more water when used for gardens or neck coolers. Crystals that are large in size won't hold anymore water.
The crystals can be dried in the sun. The sunlight will shrink them to a smaller size.