Acoustic warmth is the pinnacle of your acoustic guitar voice. Without it, your guitar will sound tinny and soulless. 80/20 bronze has 80% copper. Phosphor bronze strings contain 90% copper and because of this, has a warmer, more pleasing sound. At RED Brand Strings, they asked the question, what would 99% copper sound like. The result is RED Brand Strings, the first and only brand of copper-bronze acoustic guitar strings. With the highest copper content of any string brand, RED Brand gives acoustic guitars precise articulation, louder sound, greater projection and a warmer, richer tone. Gauges: .012 .016 .025w .036 .046 .056