A metal matrix composite comprising nanotubes; a method of producing the same; and a composition, for example a metal alloy, used in such composites and methods, are disclosed. A method for continuously infiltrating nanotube yarns, tapes or other nanotube preforms with metal alloys using a continuous process or a multistep process, which results in a metal matrix composite wire, cable, tape, sheet, tube, or other continuous shape, and the microstructure of these infiltrated yarns or fibers, are disclosed. The nanotube yarns comprise a multiplicity of spun nanotubes of carbon (CNT), boron nitride (BNNT), boron (BNT), or other types of nanotubes. The element that infiltrates the nanotube yarns or fibers can, for example, be alloyed with a concentration of one or more elements chosen such that the resulting alloy, in its molten state, will exhibit improved wetting of the nanotube material.