 The impressive mechanical behavior of protective egg capsules from Welks is due to a reversible phase transition of component protein-building blocks from a compact alpha helical confirmation to a more extended softer confirmation, called beta. However, a theoretical understanding of the non-equilibrium behaviors of the egg capsule requires a new approach. Our results indicate that hysteresis during cyclic loading originates from a mismatch between the speed of the mechanical driving force and the rate at which the phase transition occurs. The characteristic curved shape of the stress strain plot arises from a non-linear relationship between the transformation rate and the amount of applied load, which have important implications for our understanding of the mechanics of biological polymers and may have implications for the design of biomimetic pseudo-elastic polymers. This article was authored by F.D. Fisher, M.J. Harrington, and P. Fratzel.