Curt Mangan 80/20 bronze acoustic guitar strings are manufactured with 80 percent copper, and 20 percent zinc. They have balanced highs and lows. with a slightly brighter tone then phosphor bronze. FusionMatched® is Curt Mangans own tradmarked proprietary method that combines the highest quality, 100% made in the USA wire and 100% USA workmanship to produce strings with exacting core-to-wrap ratios and tolerances.