Crystal Color Stacking CupsCrystal Color Stacking Cups are an amazing resource to introduce color mixing and early STEM building concepts in the classroom or the home environment. See, hear, touch and play with these fun, lightweight cups specially designed with grooves for stacking up as high as you can build them. Then enjoy the crisp sounds they make as they topple over each other. Right side up, or upside down, the cups are easily stack able into simple or complex forms,