Two popular models for hadronic structure are bags and strings. Both involve analogies with superconductivity. We claim that the most appropriate analogies are type I superconductors for bags and type II superconductors for strings. The structures of hadrons is somewhat different for the two situations. In principle, and in practice in the real world, it is the similarities which are most important. These include linear confining potentials, linearly rising Regge trajectories and short distance Coulomb potentials. These are all generic properties of bound states in a superconductor and the main distinctions between bags and strings is under what circumstances these limiting behaviors set in.
Nair, V. Parameswaran and Rosenzweig, C., "Bags vs. Strings: Hadrons in Type I and Type II Superconducting Vacua" (1984). CUNY Academic Works.