Double-net metamaterials are virtually unexplored 3D percolating plasmonic structures that are predicted to show propagating bulk modes at arbitrarily small frequencies below the materials plasma frequency,  in contrast to other percolating metamaterial. This project aims at an in-depth investigation of those low frequency bulk modes, which are based on counter-propagating charge oscillations, similar to an electron accoustic wave (EAW) in a double plasma. Our research currently focusses on double net theory and fabrication at microwave frequencies, where the exotic EAW nature leads to new types of toplogical and bound states in the continuum. Together with the metamaterial modes project, we are further extending our understanding of EAW in double net metamaterials towards near infrared and optical frequencies.