The present disclosure provides a co-bonded acoustic liner, including a honeycomb core with cells therein, a thermoset-based plastic septa material co-bonded to a top face of the honeycomb core; a facesheet with perforations to enable airflow, co-bonded to the thermoset-based plastic septa material; and an optional backside skin positioned under the honeycomb core, co-bonded to the bottom face of the honeycomb core, wherein the liner supports a single degree of freedom acoustic structure. The disclosure further provides methods of preparing and using such co-bonded acoustic liners.