D rsquo; addario exps deliver the most natural-sounding, longest-lasting coated strings available. through our advanced exp coated technology, we have perfected the art and science of coated string-making to deliver extended play strings that sound identical to our world famous xls. plus, we rsquo; ve dramatically improved the corrosion resistance, longevity and durability of plain steel strings through an exclusive compound tin-plating process. finally...coated electric strings that deliver longer life, completely natural tone and the feel of uncoated strings. you won rsquo; t believe they are coated!