The .009 to .046 Custom Light gauge 2554 Blue Steel Electric Guitar Strings from Dean Markley are made with an 8% nickel-plated steel outer wrap over a tinned mandolin wire hex-core. During production, Blue Steel strings are cryogenically frozen down to -320°F with a blast of liquid nitrogen in order to tighten the molecules, minimizing microscopic gaps. This process is designed to create a guitar string that is more consistent, more durable, and that stays in tune longer than conventional strings. The treatment also results in greater sustain, and louder, more versatile tone.