Send your trading cards off in style. Artist Trading Cards are miniature pieces of art that are traded around the world. Artists create, trade, and collect art at organized swap events, either in person or online. The only official rule is that the trading card measures 2.5" x 3.5". These envelopes are great for mailing, gifting, or professionally presenting your work. 2.5" x 3.5". 10/Pkg. Acid-free.