Martin Lifespan MSP6200 Medium Bronze acoustic guitar strings are treated with Cleartone proprietary technology to bring you the longest possible string life without sacrificing tone or natural feel. Martin Lifespan MSP-6200 Lifespan strings are designed to repel the oils and dirt that can deaden strings. All six Lifespan M-SP-6200 strings are treated to preserve the natural Martin SP sound and feel that players prefer.