A polymer is a really big molecule made of little molecules linked together. When we placed the tiny marbles (2 millimeter in diameter each) in water, they expanded up to 10 times from its original size measuring from 10 mm 20 mm (1/4 to 3/4 inch) in diameter. Each marble can hold up to 300 times its weight in water.
The marbles bounce, because polymers are elastic like rubber. These marbles can be used for decoration.