Stiff, strong, and tough hydrogels with good chemical stability.

Most hydrogels have poor mechanical properties, severely limiting their scope of applications. Here a hybrid hydrogel, consisting of hydrophilic and crystalline polymer networks, achieves an elastic modulus of 5 MPa, a strength of 2.5 MPa, and a fracture energy of 14 000 J m-2, while maintaining physical integrity in concentrated electrolyte solutions.