Cryogenically frozen plain steel and phosphor bronze wound, loop end. Their Light gauge, 010 015 024w 038w (2 each). Sealed in corrosion-free "NitroPack" packaging. Maker says: "With feedback from players young and old, we have developed a series of strings gauged for the current needs of the musician, and then cryogenically treated them to ensure that if you're playing into the night, these sets will continue to inspire and help you share your unique voice."