Cleartone Treated Acoustic Phosphor Bronze All Cleartone Acoustic Phosphor Bronze strings are MADE IN USA at our Bountiful Utah factory using only the finest US-sourced Phoosphor bronze around a high-carbon hex core. We wind our strings under super high tension using proprietary winding methods and core-to-wrap ratios creating a denser, better sounding string with enhanced tuning stability. Lastly, we add our multi-patented award winning treatment which is scientifically proven to increase your guitar's volume and sustain by up to 36% & 48% respectively. Warm, lush, full-sounding acoustic strings with outstanding sustain are what characterize Cleartone’s award winning Phosphor Bronze series. Ultra high-carbon steel hex core covered in American made Premium Phosphor Bronze, all painstakingly wound together on our custom controlled in-house winding machines. Every string receives our twice patented Cleartone treatment, guaranteed to increase lifespan, volume output, and sustain.