Printed 6.25 x 12 Self-Sealing Cellophane Bags. Printed 6.25 x 12 Self-Sealing Cellophane Bags. Cookie Lee® Brochures fit in this size flat cellophane bag. Self-sealing makes it so easy to prepare your mailings using these envelopes. Yes, you can mail literature in our self-sealing flat cellophane bags! Also called Cello bags and cello envelopes these bags are a great business aid for direct sales professionals. We have a large selection of sizes and printed designs as well as clear cello bags. We carry cello gusseted bags, cello self-sealing bags, cello rolls and cello sheets.