LOOSE ROPE FOR CLASSIC GUITAR String Guit Esp D'addario Exp-4506. An ultra-thin layer of EXP covers the silver-plated copper cable which is wound into a multi-stranded core. The result is a weather and corrosion barrier that can quickly weaken string life and sound. EXP strings have a very natural feel and a fresh, bright sound with a new string tone that lasts three to four times longer than traditional guitar strings.