The Disk and Ring kit is made from a polymer that expands and contracts dramatically with changing temperature. It is wonderful for demonstrating the effects of thermal expansion. Submerge the disk in hot water and the ring in ice water and see what happens when you put the two back together. What would happen if you place the disk in the ice water and the ring in hot water? Disk outer diameter approximately 19 cm (7.5 inches) at room temperature.