D'Addario XL ProSteels utilize an exclusive corrosion-resistant steel alloy that delivers super-bright tone without shrill overtones. They produce brilliantly penetrating highs, rich in harmonics, combined with pronounced, tight lows. ProSteels are the ideal choice for players seeking extra bite, and sustain. Bright, loud, and aggressive, they offer a great alternative to nickel for a harder edged sound. The EPS520 super light gauge set, like all D'Addario guitar strings, come in environmentally friendly corrosion resistant packaging for freshness in every set.