Bicycle: MetalLuxe Foil 2019 Edition - Blue - Rules of Play says:

The Metal Luxe playing cards from Bicycle are one of the decks in their catalogue to feature metal (foil) decoration on the reverse of each card. These are made from premium card stock and are subject to very stringent quality checks. The quality of these playing cards is immaculate and adds an elegant look and feel to all card games, tricks and flourishes you have in your repertoire.