This chapter deals with the preparation, physical properties and structural characterisation of near-ideal amphiphilic polymer co-networks whose hydrophilic components are four-armed star poly(ethylene glycol)s (tetraPEG stars) and the hydrophobic components are either poly(dimethylsiloxane)s or four-armed star poly(ethyl glycidyl ether)s (tetraPEGE stars) or four-armed star poly[(ethyl glycidyl ether)-co-(methyl glycidyl ether)]s (tetraPEGE-PMGE stars). The aqueous swelling (including swelling and shrinking kinetics) and mechanical properties, as well as the structure of these co-networks, elucidated using small-angle neutron or X-ray scattering, are presented and discussed.