D'Addario XS Acoustic Phosphor Bronze strings combine thier most popular acoustic alloy with their most advanced string coating technology, resulting in clear tone, smooth feel, and superior tuning stability – all with the longest possible string life. With its ultra-thin film coating on every wound string and a unique polymer treatment on the plain steels, XS offers their highest level of protection for maximum life. XS also features NY Steel high carbon core and plain string wire, and their exclusive Fusion Twist, for incomparable break strength and tuning stability. XS is the most innovative coated string D'addario have ever created. Never Fade Away!