This chapter shows that the mechanical properties of amphiphilic polymer co-networks (APCNs) can be improved via interpenetration with a second hydrophilic polymer network, i.e. by employing the double-network (DN) hydrogel approach. The first APCNs in this study were based on ABCBA pentablock terpolymers comprising a middle hydrophobic polydimethylsiloxane block, flanked by two blocks of the non-ionic hydrophilic poly(N,N-dimethylacrylamide) and two end-blocks of the anionic hydrophilic poly(sodium 4-vinylbenzenesulfonate). Characterisation via uniaxial compression indicated an improvement of the mechanical properties of the DN hydrogels over those of their APCN first network precursors, with an enhancement in the strain at break and elastic modulus of up to a factor of 4 and an enhancement in the stress at break of several 100-fold. The strongest DN hydrogels exhibited compressive stress and strain at break, and an elastic modulus above 1 MPa, above 80% and above 20 kPa, respectively. Thus, the DN approach, involving the interpenetration with a hydrophilic second network, provides a facile and efficient approach to toughen APCNs.