AbstractThe assumed analogy between polymer solutions and polymer‐network gels as regards the thermodynamics of swelling—a fundamental assumption implicit in all previous analyses of swelling measurements on gels, aimed at checking the statistical theories of rubber elasticity—is shown in fact to be rather limited. In particular, excluded volume effects, which play a dominant role in both solutions and gels, are quite different in the two types of systems. A new thermodynamic description of swelling equilibria, taking account of differences in excluded volume effects, is given, and analogies and differences between gels and solutions are pointe