The effect of a woven fiberglass support layer in a composite silicone rubber membrane is examined. Flux reduction during the pervaporation process is attributed to the additional resistance offered by the support layer in both flat sheet and hollow fiber configurations. A 40% reduction (from that of the bare silicone rubber membrane) in toluene flux from a toluene-water feed solution is estimated to occur in the 0.9 mm outer diameter hollow fibers. These fibers are later used in the construction of a tubular transverse flow module to be discussed in Part II of this series.