3D reconstruction of heterogeneous ion-exchange membranes when swollen in an appropriate electrolyte by micro-computed tomography (mu-CT) can provide important information on structural changes caused, by their swelling or shrinkage and used this knowledge along with their electrochemical characteristics for optimization of the structure of these industrially important polymeric composites. We developed a methodology that allows scanning of swollen membrane samples while not being immersed in the solution, a condition necessary for CT analysis of polymeric samples. Qualitative description of membrane swelling and shrinkage induced by volume-changing ion-exchange resin particles demonstrates their strong effect on structural changes in the membrane and identifies salt concentration as one of the major factors affecting the extent to which the membrane swells or shrinks. Experimental study focused on investigating the effect of salt concentration reveals that membrane volume decreases with increasing salt concentration. The dependence between the volume of the membrane and the concentration was well fitted with a natural logarithm. This fit can be used as an empirical equation for estimating the volumetric changes of the membrane caused by immersion in salt solutions of different concentrations.