"Our new Martin SP™ Studio/Performance Series strings are ideal live, in the studio, or wherever maximum string life is desired. The creation of these new high performance strings is a result of research done in cooperation with specialty steel producers. Due to the development of an industry leading 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 does enhance the beauty of your guitar, it's purpose is much more functional - to prolong brightness, string life, and superior tonal quality to meet the high expectations of demanding musicians. Martin SP strings are available in 80/20 Bronze extra-light, custom light, light and medium gauges for 6-string acoustic guitars and an extra-light gauge for 12-string acoustic guitars."