Variations in membrane functional (permeabilities in source and receiving phases) and structural (thickness, rubber to glass transition temperature (T(g)), electrical resistance, and components' distribution) properties and transport profiles, promoted by modifications in composition that affect metal ion migration across polymer inclusion membranes (PIMs), were studied and explained through permeation, differential scanning calorimetry (DSC), electrochemical impedance spectroscopy (EIS), and reflection infrared mapping microscopy (RIMM) data for membranes with variable amounts of bis(2-ethylhexyl)phosphoric acid (D2EHPA) as carrier, tris(2-butoxyethyl)phosphate (TBEP) as plasticizer, and cellulose triacetate (CTA) as support used for In(in) removal. Quantitative expressions for most of the structural and functional properties as a function of the weight or volume fractions of the membrane components were obtained. A desirability function scheme corroborated experimental observations that a minimization in the structural properties (thickness, Tg, and membrane resistance) is followed by an increase in In(III) permeation (maximum transport with minimum retention). A progressive transition from a transport profile of the chained-carrier with reduced mobility type to a carrier-diffusion type was observed in the system due to the presence of a percolation threshold value at plasticizer content below 40% (w/w), which was dependent on plasticizer concentration. Application of the percolation theory allowed inferring that there was no constant number of neighboring sub-units next to each transport site, as confirmed by RIMM. The use of the percolation theory and PIM characterization by the different techniques allowed the conceptualization of indium permeation in relation to PIM structure. The analysis of the experimental evidence also indicated that different transport mechanisms previously reported for PIMs can effectively be integrated in terms of a more inclusive scheme that depends on membrane composition and properties for the system under examination. (C) 2011 Elsevier B.V. All rights reserved.