Ernie Ball Earthwood Phosphor Bronze MEDIUM Acoustic Guitar Strings are made from 92% copper. 7.7% tin. 0.3% phosphorus wire wrapped around tin plated hex steel core wire.  These strings provide a very smooth relax sound with a nice ring and incredible clarity.  Very popular with top high profile guitar players and anyone looking for a top quality guitar strings. At Elizondo Music we are very proud to be a direct authorized Dealer with full factory warranty.