Users who already have either RefProp 9.0 or RefProp 9.1 from NIST can use their own RefProp fluid library through FluidProp. Users who have RefProp 9.1 only need a FluidProp license allowing the use of RefProp and don't have to do anything else. Users who have RefProp 9.0 will have to add their RefProp's installation directory to their computer's 'path' enviroment variable and will also need a FluidProp license allowing it's use.