How do polymer chains behave when an elastomer is stretched and released?

When an elastomer is stretched and subsequently released, its polymer chains undergo a specific physical transition to recover their original shape:

• Under Stress: When force is applied to an elastomer, the long, irregularly coiled polymer molecules straighten out and align in the direction of the applied pull.1
• Upon Release: Once the force is removed, the molecules spontaneously return to their normal, compact, and random arrangement. This recovery is driven by the internal flexibility of the polymer chains, which allows them to return to a disordered state through the random motion of their repeating units, facilitated by rotations around carbon-carbon bonds.12

For this behavior to occur, the material must possess little internal hindrance to the motion of its subunits—meaning it must not be in a glassy state—and it must not spontaneously crystallize at normal temperatures. In many commercial applications, these polymers are vulcanized to create a loose molecular network of cross-links, which ensures the material maintains its structural integrity and elasticity without flowing like a liquid.23