There is a significant disparity between the appearance and peak-to-peak measurements between the SAXS electron density profile and the electron intensity profile obtained by cryo-ET for the thick membranes in the 50 mol% hybrid sample (Figure and 6j, respectively). The SAXS profile suggests that the thick membrane population has a peak-to-peak thickness of 110 Å, while cryo-ET suggests a measurement of 60 Å. SAXS electron density profiles also show a small electron dense peak within the centre of the trough region, which is not present in the cryo-ET electron intensity profile. Initially this feature was ignored, since it results from the choice of using two Gaussian distributions for resembling the hydrophobic core (note, in a comparable strip model this feature does not appear, see SI Section 8). However, Figure of the FFT profile from the cryo-ET images also shows the same feature but has a larger peak-to-peak measurement of 140 Å, which once more justifies the choice of our 4-Gaussian model. This suggests that the information collected by SAXS is present in the cryo-ET images, but it is too noisy (or heterogeneous) to be clearly resolved during real-space analysis. Interestingly, this central peak seen in Figure and Figure is also potentially indicative of interdigitation within thick 50 mol% PBd22PEO14 membranes.