Equilibrium swelling of natural rubber composites containing aluminium powder has been investigated in a series of aromatic hydrocarbon solvents, such as benzene, toluene, xylene, and mesitylene. These composites were vulcanized by four vulcanizing systems, viz. conventional, efficient, dicumyl peroxide, and a mixture, consisting of sulfur and dicumyl peroxide. In each system, the effect of aluminium powder with and without bonding agent was studied. The results showed that addition of bonding agent reduced the swelling considerably, and its effect is more pronounced in the conventional system due to increased adhesion. The dependence of the diffusion coefficient on the crosslinking system and the solvent-polymer interaction parameter were calculated from diffusion data. These results are also indicative of the improved adhesion with hexa-resorcinol-silica bonding system in these composites.