An micro-fine layer of EXP Coating is bonded to the phosphor bronze wrap wire which is then wound onto the hex-shaped core wire. The result is a built-in barrier against the corrosion and wear that can quickly sap the life out of your strings and your sound . EXP strings have a natural round wound feel and extra-bright tone that lasts three to four times longer than traditional guitar strings. String Gauges: Plain Steel .016, .018, Phosphor Bronze Wound .028, .035, .045, .056