# Why does rubber shrinks when it is heated?

This is a well-known phenomenon, and a proper explanation is needed. It seems counter-intuitive since common materials expand upon heating due to faster oscillation of atoms. There would be some reasoning to this observation with rubber that goes in opposite direction.

• Minor quibble: Thermal expansion occurs in common materials (e.g., metals and ceramics, whose stiffness is primarily enthalpic) because the energy curve governing bonding is asymmetric. If not for this asymmetry, then the faster oscillation would occur around the same equilibrium distance, and no expansion would occur. – Chemomechanics Jun 3 '18 at 18:06