Silky smooth sound and feel. Gauges 11.5-14-23-28-38-47. Martin M200 12-String Folk Guitar Silk & Steel Round Wound Acoustic Strings are steel strings compound wound with silk on the lower strings. The silk makes them softer to the touch and easier to play. Martin Strings are high-quality intended for daily use. Core and wrap wires must meet strict requirements to make the grade. Martin guitar strings are wound to precise specifications.