Change in length of a rubber band

It is well known that many materials, such as metals, expand when heated, as the distance between their atoms increases due to thermal energy.
However, if a rubber band that is under tension is heated, it contracts!
This is because the molecular structure of rubber consists of long, disordered polymer chains that tend to tangle up in order to maintain a state of maximum disorder (entropy). When stretched, the chains are pulled straight. In this state, entropy is lower. When heated, the molecules gain energy and move more vigorously. As the polymer chains strive to return to the more disordered, tangled state, the rubber band contracts.
In the case of a rubber band that is not under tension, there would be no significant macroscopic contraction, as the molecules are already in a state of maximum disorder.