XT phosphor bronze acoustic guitar strings from D'Addario combine acoustic alloy with an extended lifespan treatment on every string in the set, preserving the natural tone and feel of uncoated strings. This set of Light strings are ideal for all genres, but especially acoustic guitar and fingerpicking. D’Addario XT strings feature high carbon steel cores with an extended lifespan treatment on every string in the set, providing enhanced break resistance, pitch stability and performance.