The behaviour of rubber differs from that of conventional materials. Rubber heats up on stretching and cools on retraction. Also, stretched rubber shrinks on heating (thermoelastic shrinkage) while a stretched metal elongates. The elastic recovery of rubber is due to its tendency to maximize the entropy. The same property also causes the thermoelastic shrinkage. Metallic materials possess energy elasticity, while ideal rubber possesses entropy elasticity. The thermodynamic behaviour of rubber is similar to that of gaseous materials. Hence rubber can be used as an aid for teaching thermodynamics. © 2019, Indian Academy of Sciences.