Figure shows that as the polymer mole fraction increases, that the scattering intensity increases in the SAXS patterns at low q (< 0.08 Å -1 ). We note that as long as no diffraction peak is present (no underlying ordered structure exists), scattering patterns from SAXS must be fitted with a model in order to account for unilamellar membrane information. Therefore, no contribution from a structure factor was expected such that the SAXS profiles can be fitted with a form factor alone. The form factors used were adapted from a Gaussian-based model described previously. By using results from cryo-ET, physically relevant models were developed. We note that the vesicles used for SAXS analysis were dilute (6.57 mM) and displayed a PDI < 0.25 from Dynamic Light Scattering (SI Section 5).