text: The selection of the wetting liquid is important as it determines the measurable pore size range for a given pressure. Some common wetting liquids used in capillary flow porometry include water, alcohols, silicone oil and perfluoroethers. The use of water and/or alcohols present the disadvantage that they can evaporate and therefore the samples can partially dry before the actual porometry test begins. Also water, for instance, has a relatively high surface tension (γ= 72 dynes/cm) compared to perfluoroethers (e.g. γ= 16 dynes/cm), which means that  in order to measure the same pore size using water as a wetting liquid it is required to apply 4 times more pressure than when using a perfluoroethers. Silicone oil does not present the evaporation drawback but its high viscosity makes the cleaning of the equipment parts in between different measurements not easy. Perfluoroethers have very low surface tensions and low vapour pressures, which makes them immune to the problem of evaporation. In general they do not react with samples neither cause their swelling.  
  In principle there is no universal wetting liquid and the choice of one or another depends on the application and the type of sample to be characterized. Nevertheless it is important to use always the same wetting liquid when comparing results.