The present disclosure is drawn to a thermal inkjet printhead stack with an amorphous thin metal protective layer, comprising an insulated substrate, a resistor applied to the insulated substrate, a resistor passivation layer applied to the resistor, and an amorphous thin metal protective layer applied to the resistor passivation layer. The amorphous thin metal protective layer can comprise from 5 atomic % to 90 atomic % of a metalloid of carbon, silicon, or boron. The film can also include a first and second metal, each comprising from 5 atomic % to 90 atomic % of titanium, vanadium, chromium, cobalt, nickel, zirconium, niobium, molybdenum, rhodium, palladium, hafnium, tantalum, tungsten, iridium, or platinum. The second metal is different than the first metal, and the metalloid, the first metal, and the second metal account for at least 70 atomic % of the amorphous thin metal protective layer.