This listing is for a pack of 100 Supersafe Museum Grade Postcard Sleeves for4" x 6 1/4" post cards (MG480). Supersafe MG (Museum Grade) series Postcard Sleeves are made from 4 mil Mylar. The Mylar polyester film makes these Postcard Sleeves ideal for long term storage. These holders open on the left and right and also can be opened at the top for easy insertion. The tops fold over for added protection. Each Postcard Sleeve holds a single post card. These Postcard Sleeves are new from our inventory.