These curious growing spheres are made from a chemical known as super absorbent polymer (or SAP). SAPs are amazing materials. They are long chains of molecules that join together in a net-like pattern. Water is pulled in through the holes of the net then the molecule chains soak up tremendous amounts of water.
When the molecules absorb water, they swell and soften and transform into a hydrogel. Swell! D: 1.38.