From D'Addario:

Silk and Steel were uniquely designed to be our warmest, mellowest acoustic guitar string. Ideal for parlor guitars and vintage instruments, the softened tone of Silk & Steel is often preferred by folk players. Made with silver-plated copper windings, over a combination silk and steel core, the low tension and reduced finger noise of Silk & Steel is well suited for mellow acoustic vibes and fingerstyle playing. This 11-47 Light set is easy to play and provides a warm tone.