Cleartone Coated Bass Strings are made of nickel-plated steel over a hex core. A unique treatment called EMP coats the entire string with an ultrathin protective film. It's the thinnest coating ever applied to bass strings (less than one micron!) and will withstand more abuse from hard strumming than coatings 1000 times thicker! EMP ensures longer string life by protecting strings from corrosion due to skin acidity, salt, and moisture without compromising feel and sound. Made in the USA.