The magic of this experiment lies in polymers. Polymers are long chains of molecules that make up many items we use in our everyday lives – specifically plastic items. Ziploc bag, plastic grocery bags, and plastic food packaging are all made of polymers. Products made of polymers are flexible and leak-proof. Think of polymers as long chains of beads. When you stab a pencil through the bag, the polymers move apart. Because polymers are flexible, when you stab a pencil through the bag, the polymers push back toward the pencil and form a temporary seal. This prevents the water from leaking out of the holes. If you remove the pencils from the bag, the holes will remain in the bag because you have permanently pushed the polymers aside, allowing water to leak out.