These D'Addario Chromes have nickel-plated steel underwindings on hex cores with a delicate stainless steel outer ribbon winding. After winding each string is given 3 polishing steps to produce a smooth surface, each string is wound and polished on the same machine with string tension remaining constant between processes. These light gauge jazz strings are possibly the smoothest strings you'll ever play. These are perfect for traditional jazz, rockabilly twang, R&B, fusion, and some pop/rock styles. The gauge is medium, .013, .017, .026w, .035, .045, .056. D'Addario's are the preferred string by many artists and professionals. They will probably be your favorite, too. One of my Teles that I bought from a jazz player was setup with flatwounds. It sounds so good and plays so effortlessly that I have always kept flatwounds on it. It is one of my favorite guitars to play.