The D'Addario XSAPB1353 is a coated phosphor bronze acoustic guitar string set in a hybrid-light gauge, .013-.053, combining lighter-tension wound bass strings with heavier plain treble strings for added projection. An ultra-thin XS film coats the wound strings and 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 tone. Made in the USA.