Reminding observers of erupting volcanoes, Sensory Bubblers intrigue all ages. The tiniest of bubbles form, float, and swirl upward. While simple scientific principles explain the phenomenon, a sense of magic lingers. A mixture of mineral oil and colored water fills a crystal clear, hour-glass shaped center cavity. Easy to grasp, thin yet rigid, textured plastic. Rounded edge end-caps. Lightweight and easy for children to hold. Ideal distraction toy. Perfect for quiet concentration as well as inspiring curiosity and developing creative language. Four-pack contains one each of red, yellow, green, and blue. Bubblers measure 3 1/2″L x 4 7/8″H. Also sold singly.