From the manufacturer:
Add reflective shine to your handwriting and illustrations. Metallic has a distinctive reflective sheen, similar to the bright colors of polished hot rods. This shiny, opaque Gelly Roll® writes on both light and dark papers as well as glossy and matte surfaces. Additionally, Sakuras archival quality gel ink ensures that your work (and the metallic sheen) will last for years. So put pen to paper and create an artistic, polished mark thats uniquely your own.