Do you want to get your students fired up about refraction? Try Jelly Marbles. Starting out as tiny, super-absorbent beads, Jelly Marbles swell to 300 times their original weight when placed in water. With an index of refraction identical to that of water, Jelly Marbles become completely invisible when submerged. Just imagine how your students will react when they stick their fingers into a water-filled bowl only to learn that the bowl contains something unexpected! A package of Jelly Marble crystals, which are great for demonstrating a wide range of refraction effects, comes with suggestions for activities.