All polymers have a distinctive degree of elasticity — how much they will stretch when a force is applied. However, for the past 100 years, polymer scientists have been stymied in their efforts to predict polymers’ elasticity, because the materials usually have structural flaws at the molecular level that impact elasticity in unknown ways. By coming up with a way to measure these structural defects, MIT researchers have now shown that they can accurately calculate the elasticity of polymer networks such as hydrogels.