Abstract: A composite hyperconductor for use at cryogenic temperatures and particularly well suited for AC applications employs at least one filament of conductor having an extremely low electrical resistance at cryogenic temperatures, a strengthening matrix surrounding the conductor, and a barrier for electrically insulating the conductor from the matrix while providing for efficient heat transfer therebetween and/or serving as a diffusion barrier to prevent contamination of the high purity conductor during processing. The preferred composite hyperconductor for space applications comprises an ultra high purity aluminum conducting filament, a aluminum alloy matrix and a boron nitride barrier.