Significance Life requires a delicate balance between cell membrane rigidity and fluidity to define cell boundaries yet enable cell deformation, growth, and division. Here, we bridge the molecular and macroscopic scales with neutron scattering techniques to demonstrate how the material properties of model lipid membranes are readily tuned by the constituent lipid composition. Mixing lipids leads to softer and less viscous membranes than predicted a priori from the pure component membrane properties. Instead, the dynamics are linked to the membrane structure and follow simple scaling relationships with the area per molecule. These results emphasize the importance of lipid packing and reveal the interwoven relationship between lipid membrane structure and dynamics.