225 x 318 mm plastic envelopes. Pack of 200. Royal Mail Large Letter (A4) size. Our grey polythene mailing bags are great value economy mailers that do not compromise on quality. Suitable for a multitude of mail order products. Popular across a wide range of industries including mailing, catalogue and internet companies. Ideal for sending items through the post or via a courier. Each mailing bag has a polythene lip with an easy to use peel-and-seal strip. The polythene is 55 micron (220 gauge) thick.