In this paper, we present the results of variations in the bulk solvent type and the addition of cosolvents on the growth rate of metallic copper nanoparticles produced through a reduction reaction within AOT reverse micelles. The metallic copper particles were characterized using both UV-vis spectroscopy and TEM microscopy. Growth rates are discussed in terms of an absorbance ratio, which provides a correlation between UV-vis absorption spectra and particle size. Time-resolved measurements showed that the intermicellar exchange rate and subsequent particle growth rate is a function of water content, bulk solvent, and the addition of cosolvents and cosurfactants. The copper particle growth rate was found to increase with increasing water content, but essentially the same particle size was eventually approached at all water contents. Copper particle growth was faster in isooctane than in cyclohexane because of the structure of the bulk solvent and the resulting degree of solvation into the micellar tail region. The cosolvent 1-octanol was found to decrease the copper particle growth rate when added in small amounts (up to 3 mol %) at two different water contents, but larger amounts of the cosolvent destabilized the micelle, increasing the growth rate and decreasing the terminal particle size. The cosolvent benzyl alcohol had the opposite effect, increasing the copper particle growth rate and decreasing the terminal particle size at all of the concentrations studied.