The most common material for steel string acoustic guitars. This string has the brightest sound when new. However it will loose its initial brightness very quickly. This can be an advantage. If you don't want a bright sound, play on these strings for a few hours and they will start to mellow.

Phosphor Bronze Wound

This type of string is a bronze string with phosphor added to the alloy. This has two primary effects. It will make the string warmer sounding than regular bronze, and will extend the life of the tone (Will maintain its original sound longer). Phosphor Bronze Wound strings are widely used on steel string acoustic guitars.

Silk & Steel is a special design string for steel acoustics where the unwrapped strings are plain steel and the wrapped strings have a thin steel core surrounded by many nylon filaments and then wrapped with silver plated brass windings.