Place these hard crystals in water and they expand about 300 times, producing gel-like spheres. Students love to feel the slippery, spherical gel! The Large size start with a diameter of about 3.0 mm and end with a diameter of about 20.0 mm. Ask students to determine the change in volume, using V = 4/3 pr3. Great for starting seeds and growing plants so that the roots can be seen! Can be colored using food coloring. The polymer is similar to our super-absorbent, polyacrylamide polymer (#GB-5B and #GB-3) and can be dried and reused. Now available in three sizes: Regular (~1.4 cm expanded), Large (~2.3 cm expanded), and Jumbo (~3.3 cm expanded)! (Each package contains 50 grams.)