Built under the direction of Gibson's famed acoustic luthiers, Gibson Masterbuilt Premium strings are phosphor/bronze-wound to give your acoustic guitar a bright attack and sustained warmth that's perfect for the ultimate acoustic sound. Just like their instruments, Gibson strings are "American Made, World Played" and each set utilizes strict quality control methods to ensure tone, durability and consistency. All authentic Gibson strings feature specs absolutely unique to Gibson and are factory sealed to guarantee freshness in every set.