A reversible polymer that glows under stress would offer an early warning sign of structural damage.
Although other polymers have been created that alter visibly under stress, they can usually only alert once, and can also be confused by false alarms.
In contrast, the new polyurethane polymer relies on dumbbell-shaped molecules with fluorescent macrocycles threaded onto it. The macrocyles will group together in the middle of the dumbbell when the polymer is relaxed, where adjacent quencher molecules prevent them from fluorescing. However, stretching the polymer will pull the macrocyles away from the quenchers and cause them to glow under ultraviolet light, with the intensity of the glow relative to how much the material is stretched. The glow will subside when the tension is released, and the process can be repeated indefinitely.