Since D'Addario introduced Phosphor Bronze acoustic guitar strings in 1974, they've been synonymous with warm, well-balanced tone. XT Phosphor Bronze offers that and more, boasting enhanced break resistance, better pitch stability, and longer life than our standard phosphor bronze strings. The XT coating delivers advanced corrosion resistance, while still retaining the warm tone and natural feel of the uncoated string. Beneath the coating, these XT acoustic strings are constructed with a NY Steel core, phosphor bronze wrap wire, and Fusion Twist technology, affording tonal versatility with added resilience, excellent for a wide range of acoustic styles. These 13-56 Medium gauge strings provide maximum volume and projection, with more tension and resistance. D’Addario XT strings feature high carbon steel cores with an advanced corrosion resistance treatment on every string in the set, giving you enhanced break resistance and unyielding pitch stability—all while preserving the tone and feel of your favorite uncoated strings. These strings are made to stay, with uncompromising performance that never fades away.