D'Addario XSE1149 Electric Strings 

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 our 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 our exclusive Fusion Twist, for incomparable break strength and tuning stability. XS is the most innovative coated string ever created