XT acoustic phosphor bronze strings combine our most popular acoustic alloy with an extended lifespan treatment on every string in the set, preserving the natural tone and feel of uncoated strings. Available for 6 and 12-string acoustic guitar ranging from extra-light to medium gauges to suit a variety of Playing styles and preferences. Addario XT strings feature High carbon steel cores with an extended lifespan treatment on every string in the set, giving you enhanced break resistance, pitch stability, and long-lasting performance – All while preserving the tone and feel of your favorite uncoated strings. These strings are made to stay, for performance that never fades away.