Comparing the pure POPC lipid profiles, the peak-to peak positions from both SAXS, cryo-ET, FFT and SPA have excellent correspondence, where peak positions are closely aligned as shown by Figure . In the SAXS profile, the peak-to-peak distances in POPC lipid membranes is 36 Å, while for the cryo-ET profile, the peak-to-peak distance is 34 Å (see SI . The FFT and SPA profiles give peak-to-peak measurements of 35 Å and 41 Å, respectively. All these measurements are comparable to the peak-to-peak and membrane thickness measurements of POPC lipid membranes found previously using SAXS and cryo-TEM: in SAXS, the peak-to-peak distance was estimated to be approximately 38 Å, while measurements of cryo-TEM images gives a membrane thickness of 37 Å. Both SAXS and cryo-ET reveal two bilayer populations within the 50 mol% PBd22-PEO14 hybrid vesicles, one population presenting a thinner membrane < 65 Å (Figure the peak-to-peak distances for the thin membranes is 36 Å, while for the cryo-ET profile, the peakto-peak distance is 36 Å. The FFT and SPA profiles give peak-to-peak measurements of 40 Å and 39 Å, respectively. The FFT profile in Figure also shows a small electron dense peak within the centre of the trough region, potentially indicative of homogenous hybrid membranes as well as interdigitation within these membranes. As previous studies have shown well mixed hybrid vesicles form from POPC/PBd22PEO14 mixtures, polymers present in both the inner and outer bilayer leaflets of these thin membranes would tangle to reduce exposure of their hydrophobic region to water. This region would then have a higher electron density due to interdigitation, than if the polymer leaflets were completely segregated.