Ernie Ball Everlast Coated Acoustic Guitar Strings use advanced nanotechnology to repel moisture and oils that can affect your tone. This treatment protects both the inner hex core and outer wrap wire without sacrificing tone or feel. Made from 92% copper, 7.7% tin, and 0.3% phosphorus wrapped around a brass-plated hex steel core, these phosphor bronze strings produce warm bass tones and clear, bright trebles.