Variation in lipid composition between different biological membrane and across membranes are vital for a wide range of cellular functions. Significant differences in lipid distribution have been found between different organelles and cells, yet the mechanism and rate of phospholipid flip-flop (movement of a lipid from one leaflet to the other) and exchange (movement of a lipid from one membrane to another) are currently very difficult to measure, and estimated rates span several orders of magnitude. Labelling lipids (e.g. with fluorescent groups) significantly affects the kinetics of these processes and so it is extremely important to develop chemical-label free methods to elucidate their mechanisms and kinetics. We aim to apply a neutron contrast variation based to probe the mechanism of inter-vesicle lipid exchange and intra-vesicle flip-flop, and systematically measure their rates.