This obviously works best with the strings completely off the guitar, but just slackening them until they are well off the board will suffice. The polishing pads themselves are made from some kind of fibrous paper material, and the cool thing is, unlike steel wool, there are no worries about stray strands getting stuck to your pickups or polepieces to cause electrical havoc.
Choosing a neglected ax with unusually tarnished frets, I laid the cardboard cutout down, and rubbed each fret until a gleam was present. The amount of funk left on the pad was surprising—this stuff works—and my guitar’s frets once again felt clean and smooth. If your frets have lost their luster, give this system a try. You’ll dig what it does.