Amphiphilic ABA triblock copolymers, such as poly(2-methyloxazoline)-block-poly(dimethylsiloxan)-block-poly(2-methyloxazoline) (PMOXA-PDMS-PMOXA), form vesicular structures. Here, the interaction of these ABA molecules with lipids is investigated by electron microscopy, fluorescence spectroscopy, light scattering, and differential scanning calorimetry. Our observations suggest the formation of homogeneous mixed polymer-lipid composites, independent of preparation method, i.e. film hydration, dispersion, or detergent removal. When ABA polymersomes and liposomes are mixed, we observed monomer exchanges on a time scale of minutes. The possibility of forming mixed structures and the exchanges between preformed structures allow the combination of the properties of lipids and polymers such as stability and loading encapsulation capacity.