In biological membranes compositional asymmetry across organelles as well as between two contiguous leaflets belonging to the same membrane is essential for function. The passive movement of lipids tends to uniformly distribute and homogenize membranes. This is energetically helpful during the distribution of lipids across the cell but it is not helpful when gradients have to be maintained. Gradients are maintained by the active work of proteins that act against homogenization. The work needed depends on the transport characteristics of these lipids. The energetics of the passive movement of lipids in membranes gives the protein-assistance burden necessary to keep the lipid compositional gradients required for function. Using TR-SANS we were able to measure the flipping and exchange rates of cholesterol and lipids and found them to be slow. In order to decouple exchange and flipping rates we used TR-NR to find that the flipping rates, however these were fast. We believe the surface and curvature are having a strong effect. We propose to use membrane coated silica nano particles to confirm these effects.