A single model was used to fit the pure lipid and polymer systems (the 3 Gaussian and 4 Gaussian functions of Eq 1 and 2, respectively). However, for the hybrid POPC-PBd22-PEO14 membranes, a combination of the two models was required to account for contributions from both membrane structures. Led by the measurements obtained using cryo-ET, two models were fitted to the hybrid membranes resulting in both thick (Eq. 2) and thin (Eq. 1) membrane electron density profiles for each hybrid vesicle sample. For hybrid samples, a weighting factor, 𝑤, was applied for the fraction of the thick membrane vesicles in the hybrid sample (with (1 -𝑤) indicating the fraction of thin membrane vesicles):