A novel experimental technique, namely tapered element oscillating microbalance (TEOM) is utilized to study the effect of equivalent weights (960-1200), temperature (30-90 degrees C), various cationic forms (H+, Li+, Na+, K+ and Cs+), sorbates (water, methanol, ethanol and propanol), and inorganic additives on sorption behavior of Nafion (R) membrane. It is observed that water sorption increases with a decrease in EW and an increase in the sorption temperature. This is due to the increase in acid sites for sorption and a decrease in the Young's modulus of the membrane with the increase in temperature. Further, sorption decreases with the increase in size of the counter ion due to a corresponding decrease in ion hydration capacity due to a decrease in the ionization equilibrium constant constant. Also, it is observed that the incorporation of acidic inorganic additives (ZrO2, TiO2 and SiO2) via so] gel methods provides higher water sorption amount at 90 degrees C, which is crucial for higher temperature operations of fuel cells. (c) 2005 Elsevier B.V. All rights reserved.