The problem of hydrogen embrittlement, which adversely affects the quality and mechanical properties of electroformed iron-nickel alloy foil, is considered. Heat-treatment, such as annealing, can reduce these effects of hydrogen embrittlement. The electroformed metal can also be converted to alloy steel by carburizing; and by other heat-treatments, such as hardening and tempering, a range of mechanical properties for the foil can be achieved.