Phosphor bronze, It is an alloy of cooper 90% and 10% zinc and last longer than conventional bronze alloy strings. Also the small percentage of phosphorous in the alloy helps them to retain their sound longer. The strings vibrate more consistently and with greater amplitude to produce a sharper, more precise tone.
Guage Details:
E -1st: .011 Plain Steel
B-2nd: .015 Plain Steel
G-3rd: .023 Phosphor Bronze
D-4th: .030 Phosphor Bronze
A-5th: .039 Phosphor Bronze
E-6th: .050 Phosphor Bronze