Development of tough hydrogels has greatly expanded their applications as load-bearing materials. However, the elastic modulus of tough hydrogels is usually lower than 1 MPa. It remains a challenge to design tough hydrogels with high modulus. We report here a series of tough double-network (DN) hydrogels with ultrahigh elastic modulus (up to 200 MPa) by forming robust hydrogen bonds between the first poly(acrylic acid) network and the second poly(N-isopropyl acrylamide) network. The dense cooperative hydrogen bonds greatly reduce the segmental mobility and thus improve the rigidity of gel matrix. Owing to the dynamic nature of hydrogen bonds, the modulus of hydrogels is strongly influenced by temperature and pH, affording the gels shape memory property. The strategy by forming robust noncovalent bonds between interpenetrating networks should be applicable to other systems for designing tough and versatile hydrogels with diverse promising applications. (c) 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018, 56, 1281-1286