Like other parameters extrapolated to infinite dilution, the intrinsic viscosity describes the interaction of a single average polymer molecule with a sea of solvent. For a spherical molecule, [η] should be proportional to the molecular volume. For many synthetic polymers in dilute solution, the chains tend to adopt a tight, ball-like configuration in solution, the average structure of which is defined by a radius of gyration, RG. For such molecules, one predicts that: