Predicting the permeability of natural rubber (NR), carboxylated styrene-butadiene rubber (XSBR), and NR/XSBR latex membranes has been investigated with special reference to the effects of the blend ratio, the pressure, and the nature of the permeants with oxygen and nitrogen gases. These blend membranes are a new class of materials that combine the excellent mechanical properties of NR and the weather and solvent resistance of XSBR. NR shows higher permeability than XSBR latex films. This is associated with the high extent of the flexibility of the NR network due to its very low cohesive forces of interactions. The experimentally determined permeability values have been theoretically correlated with the Maxwell, Bruggeman, and Bottcher models. The oxygen-to-nitrogen selectivity decreases with an increase in the XSBR content in the blend. Attempts have been made to correlate the transport characteristics with the morphology of the blend. (c) 2005 Wiley Periodicals, Inc.