Guitar Accessories . A micro-fine layer of EXP coating is bonded to the 80/20 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. Coupled with our compound-plated plain steels, EXPs are the longest lasting, most natural sounding coated strings you can buy.