Martin Lifespan SP Bronze 12-54 MSP6100 Light Martin SP Lifespan strings are the next level in studio performance. Treated for long life, they repel dirt, grit and other environmental elements that can quickly alter the sound of your strings. The treatment is so incredibly thin, you won't even know it's there. SP Lifespans are designed to last longer and sound better so you can play on! Martin SP Lifespan 80/20 Bronze acoustic guitar strings are made with bronzed steel core wire and bronze wrap wire, then all six strings are treated for long life.