The ion exchange capacity of recast Nafion films and composites of Nafion and polystyrene microbeads is determined by titration. Composite formation enhances exchange capacity; exchange capacity increases with the surface area of microbeads in the composite. For recast films, an equivalent weight of 996 +/- 24 is found, whereas the lowest equivalent weight (highest exchange capacity) found for a composite is 878 +/- 8. This suggests that greater than or similar to 13% of the exchange sites within recast films are inaccessible for ion exchange; for 1100 equivalent weight material, greater than or similar to 25% of the sulfonates are inaccessible. Equivalent weight results are consistent with an ordered interfacial domain between Nafion and the microbeads. A fractal model based on microbead radii, microbead fraction, and interfacial domain thickness provides a predictive model for designing composites with increased exchange capacity and cation transport.