D'Addario unveiled part of their secret manufacturing process for EXP Extended Play Coated acoustic guitar strings by describing that a special coating is applied before the phosphor bronze wrap wire is wound on a high-carbon hex core. It is said that because the wrap wire is coated first, the strings retain the same feel and sound of regular bronze and last up to four times longer. Apparently these strings were time-tested under the extreme conditions of smoky and beer-soaked bars in Ireland. They held their sound and brightness for over four consecutive nights in this torturous, test situation.