The production of stable, pre-reactive, nanocomposite mixtures of magnesium and a perfluoropolyether (PFPE) has been achieved through the application of helium droplet cluster assembly. The nanocomposite films presented in this work demonstrated clear thermal desorption features that indicate the formation of an MgF2 passivation layer between unreacted magnesium cores and PFPE shells upon heating. Additional heating resulted in the later rupture of the MgF2 layer and release of trapped magnesium. The passivation behavior occurred only after deposition with the input of thermal energy, demonstrating the ability of helium droplets to assemble and deposit clusters in a pre-reactive state.