presents a particularly intriguing case in this respect. Stretching a piece of natural rubber at room temperature turns the amorphous rubber into a semicrystalline material. These crystallites are highly oriented along the tensile direction and, acting like filler particles or crosslinks, tremendously elevate the tensile strength (fig. 1). The tire industry takes advantage of these outstanding mechanical properties, using compounds high in natural rubber for truck tires to extend the tire lifetime. Due to the local reinforcement of strain-induced crystallites at the highly strained crack tip, the crack growth resistance in natural rubber is orders of magnitude higher than in conventional synthetic non-crystallizing rubbers (fig. 2).