where, d t and d h are the tail group layer and head group layer thicknesses respectively, and V t and V h are the tail group and head group volume respectively. The purpose of this constraint is to ensure that the molecular structure of the phospholipid molecule is conserved, such that there is one head group for each tail group. The scattering length density for each of the head and tail groups are then evaluated as in Equation ??, where the scattering length values for the head (h) and tail (t) groups are taken from Table . The values of V t and V h were taken as 850.4 Å3 and 339.5 Å3 respectively, as discussed for model 1. The thickness of the head group layer is defined based on the molecular dimensions, in agreement with Campbell et al., with a value of 10 Å and again the roughness is kept constant at 2.9 Å. The variable parameter in this model is the thickness of the tail group layer, d t , which was given a uniform prior probability from Å. For all of the neutron reflectometry analyses, the model was co-refined against up to seven experimental datasets, as is discussed in Section III the number of datasets was varied to assess the information content of the experimental technique. This co-refinement involved all of the structural variables (all variables except the scattering lengths b h/t/l ) being constrained to be the same values across all of the different contrasts measured. In all of the , the colour transparency represents the volume fraction (φ) of a given component, d is the phospholipid layer thickness, and dt is the phospholipid tail layer thickness. This figure file is available under the MIT license as part the electronic supplementary information . models, the resultant reflectometry was scaled and a uniform background was added on a per contrast basis. The values used for the scaling factors were taken from the previous analyses of these datasets, namely the work of McCluskey et al. , while the background level was set as the lowest reflected intensity measured in the reflectometry profile. We accept that this assumption could impact the results of a given analysis, however, the same assumption was applied for all models.