Like all the Martin SP Studio/Performance Series strings, the MSP4150 SP Phosphor Bronze Light/Medium acoustic guitar strings are ideal live, in the studio, or wherever maximum string life is desired. The creation of these high-performance Martin strings is a result of research done in cooperation with specialty steel producers. Due to the development of a top-notch ultra-high quality steel core, Martin SP strings resist breakage better than average strings. In addition, both the core wires and the plain strings are plated with a smooth, acoustic bronze finish. Though this golden bronze finish will enhance the beauty of your guitar, its purpose is much more functional—to prolong brightness, guitar string life, and provide superior tonal quality to meet the high expectations of demanding musicians.