In recent monolayer measurements, we have developed models for obtaining detailed structural information of phospholipid structures. The models employ a 'quasimolecular' approach, where the reflectivity data is analyzed using realistic molecular models of the lipids. The advantage of these models is that they can be easily applied simultaneously across multiple contrasts, allowing highly detailed structural information to be obtained from reflectivity data.We now wish to repeat these studies with the more complex, physiological case of bilayers rather than monolayers. The ISIS model membrane system - the Free Supported Bilayer (FSB) - is now reliable and robust enough that a detailed, simultaneous analysis of multiple part-deuterated samples can be contemplated. These measurements will allow us to develop detailed models for better analysing bilayer data from ISIS reflectimeters.