The D'Addario XSAPB1356 is a coated phosphor bronze acoustic guitar string set in a medium gauge, .013-.056, providing greater volume, projection, and tension. An ultra-thin XS film coats the wound strings while a polymer treatment protects the plain steels for extended life and a smooth feel. The set uses phosphor bronze wrap wire over an NY Steel core for warm, balanced acoustic tone and tuning stability. Made in the USA.