A wound string has two main parts:
- Core wire: the center wire that forms the foundation of the string. It largely determines flexibility, strength and overall feel.
- Wrap wire: the outer wire wound around the core. It plays a major role in tone, texture, brightness and playing response.
Smaller strings can be made from a single piece of wire, which is why the highest strings in a set are plain. Larger strings use wound construction to reach a greater diameter while staying flexible and playable.
Construction choices influence tone, sustain, flexibility, attack, harmonic content and playing response. That's why two strings with the same gauge can feel different. Core wire size, wrap materials, construction methods and manufacturing techniques all affect feel and tone, even when the gauges match.