AbstractNanothermites have shown the potential to controllably fracture substrates in applications such as electromechanical systems security. In prior work, both equivalence ratio and material formulation have been varied to tailor fracturing performance. In this paper, material confinement was utilized to further tailor the fracturing performance of aluminum bismuth (III) oxide (Al/Bi2O3) and aluminum copper (II) oxide (Al/CuO) nanothermites. These nanothermites were selectively deposited onto representative substrates through inkjet printing. Al/Bi2O3 nanothermites were prepared over a range of equivalence ratios and showed a range of resulting fragmentation, with a maximum near the equivalence ratio of ϕ=2. Burning rate measurements correlated with the trends seen in these experiments. All of the previous attempts at fragmenting a substrate using unconfined Al/CuO were unsuccessful. The prepared Al/CuO nanothermites at stoichiometric conditions resulted in fractured silicon substrates when confined. These results demonstrate the ability of confinement to further tailor the fracturing performance of nanothermites.