The Ernie Ball 12 String Slinky Electric Guitar Strings have wound strings made from nickel plated steel wire wrapped around tin plated hex shaped steel core wire and the plain strings are made of specially tempered tin plated high carbon steel producing a well balanced tone for your guitar. Their signature recipe consists of specific gauges and core to wrap ratios for balanced, rich harmonics and that signature slinky feel. They're made by Ernie Ball in their California factory using state of the art winding technology for consistency and reliability and are packaged in their watertight element shield packaging to resist humidity and keep your strings factory fresh.