Please note that this envelope size is not able to be mailed via USPS. Use these to send flat, bulky materials or multiple small items like coins, catalogs and jumbo cards. The flap is on the short side, helping to keep things from falling out after ope ning. Also called a "catalog" envelope, these actually come in 39 sizes from tiny to huge, in white, traditional kraft, for a special impact. They are available with a moistenable flap or with self-stick peel and seal.