The enhanced sampling brought about by the decreased viscosity of the TIP3P-F model is less than what we observed for small biomolecules. The reason for this is that lipid mobility is dominated by the membrane viscosity. To speed up the lipid dynamics more substantially, one could use mass repartitioning and scaling also for lipids. Figure : Mass density profiles of the lipid headgroups, glycerol backbone, acyl chains and water in simulations of POPC bilayers using the TIP3P (solid lines) and TIP3P-F (dashed lines) water models. For the analysis of the water mass density, standard water masses were used in both cases. We demonstrated that decreasing solvent viscosity enhances conformational sampling in biomolecular simulations. The substantial speedup in sampling by about a factor of two for solvated biomolecules, proteins and nucleic acids, and by ∼ 25% for fully hydrated lipid bilayers afforded by the TIP3P-F model is achieved without compromising the structural and thermodynamic properties of solute and solvent.