In 1974, D'Addario introduced Phosphor Bronze strings for acoustic guitars. Today, the Phosphor Bronze is considered the standard for acoustic guitar strings, due to its balanced tone and warmth. The Phosphor Bronze acoustic guitar strings are precisely wound with phosphor bronze wire over a high-carbon steel core, offering tonal flexibility suitable for all acoustic styles and genres. The 09-45 Super Light set is D'Addario's lightest gauge for acoustic guitar, providing easy playability while maintaining sufficient tone and projection for most playing situations.