These are Golden Age size (7-3/8" x 10 1/2" with a 2" flap) (or 193.67mm x 266.7mm) comic sleeves. The sleeves are 2 millimeters thick and are made of polypropylene. The sleeves have a flap on them that help protect the comics from wear. The flap can be closed with tape or with a store label. These work perfectly with our Golden Age Boards. Golden Age Comics are the period beginning with Action Comics #1, published June 1938, and ending with World War II in 1945. They are bigger than Silver Age Comics, which came next, and bigger than comics currently made. These bags are perfect for protecting your Golden Age comics from wear and tear!