The new Martin SP+ Extended Life Strings are specially coated offering a clear, rich, and long-lasting sound as well as numerous benefits, including protection from moisture, salts, perspiration and other contaminants. In addition, the new SP+ coating helps insulate the wrap wire to prevent corrosion between the core and the wrap wires. Martin uses computerized equipment in a climate controlled environment to verify the high tensile strength of all incoming wire prior to manufacture. The brass wrap is then carefully spun onto the core wire for the four wound strings of each set. SP+ strings use the same special brass plated core wire that is incorporated in the innovative SP string, but the brass wrap on the four wound strings is specially coated. With the coating, the surface of the string feels smoother and faster for the player.