Built to achieve unmatched tone and playability, Martin Era™ strings set a new standard for what a phosphor bronze acoustic guitar string can be. Combining the best technologies from the Martin Strings lineup, Martin Era strings feature a patented Lifespan® treatment to protect against corrosion, Flexible Core construction to enhance fretability and comfort, and silk-wrapped ball ends-designed with vintage instruments in mind and as a premium touch that symbolizes Martin's handcrafted string-making history. The Artist Light version was developed in collaboration with six-time GRAMMY® winner Jason Isbell and features a more traditional SP® core to match his signature guitar sound.