Three types of experiments were performed on an Al/CuO nanoscale thermite to understand the effect of adding a diluent (40 nm Al2O3 particles) to the mixture: the constant volume pressure cell, the unconfined burn tray, and the instrumented burn tube. The addition of Al2O3 decreased the pressure output and reaction velocity in all three experiments. Burn tube measurements showed three reaction velocity regimes: constant velocity observed when 0% (633 m/s) and 5% (570 m/s) of the total weight is Al2O3, constant acceleration observed at 10% (146 m/s to 544 m/s over a distance of 6 cm) and 15% (69 m/s to 112 m/s over a distance of 6 cm) Al2O3, and an unstable, spiraling combustion wave at 20% Al2O3. The pressure measurements correlated to these three regimes showing a dropoff in peak pressure as Al2O3 was added to the system, with relatively no pressure increase observed when 20% of the total weight was Al2O3. Equilibrium calculations showed that the addition of Al2O3 to an Al/CuO mixture lowered the flame temperature, reducing the amount of combustion products in the gas phase, thus, hindering the presumed primary mode of forward heat transfer, convection.