These Pro-Mold Magnetic Card Holders have a recessed area that is large enough to accommodate the included, specially-sized sleeve. These sleeves are an added layer of protection for the enclosed card. This is especially important if you are protecting a shiny foil card, as the foil layer can get scratched if dust was on the card when it was placed in the magnetic. Using a sleeve minimizes the chance of the foil card getting scratched. There are many branded and hobby community names for these reflective foil cards, including: Chrome (Topps Bowman), Refractor/Superfractor (Topps), Optic (Panini), silver, rainbow, reflective, holo, Prism (Panini), Pulsar (Panini), colored refractor parallels, and more.