Reminding observers of erupting volcanoes, Sensory Bubblers fascinate both children and adults. The tiniest of bubbles form, float, and swirl upward. As if by magic. Nevertheless simple scientific principles explain the phenomenon. Constructed of thin yet rigid textured plastic. Rounded edge end-caps eliminate sharp corners. While a nontoxic mixture of mineral oil and colored water fills the crystal clear, hour-glass shaped center cavity. Lightweight and easy for children to grasp and hold, Sensory Bubblers make ideal distraction toys. Perfect for quiet concentration as well as inspiring curiosity and developing creative language. Bubbler measures 3 1/2″L x 4 7/8″H. Four pack includes one each red, yellow, green, and blue. Don’t need four? Then Sensory Bubbler is for you.