D’Addario XS Phosphor Bronze Coated Acoustic Guitar Strings have the longest life of any D’Addario acoustic guitar string. The XS coating gives our warm, balanced Phosphor Bronze strings maximum life, with an uncommonly smooth feel. Made with a NY Steel core, Phosphor Bronze wrap wire, and Fusion Twist technology, XS coated acoustic guitar strings have incomparable break strength and tuning stability, in addition to their dramatically increased lifespan. 12-53 Light strings are our most popular acoustic gauge, providing a nice balance of playability and tone. XS is breathing new life into coated strings. With its ultra-thin film coating on every wound string and a unique polymer treatment on the plain steels, XS offers the highest level of protection, for maximum life with an uncommonly smooth feel. XS also features NY Steel high-Carbon core and plain string wire, along with exclusive Fusion Twist, for incomparable break strength and tuning stability. XS is the most innovative coated string ever created.