When shipping posters and paintings it is important that they are protected properly, so they will not be damaged during transportation. Send the poster in a triangilar cardboard tube or use the quattropac square cardboard tube when sending big stacks of posters. The standard round tubes comes in black for expensive looking shipment, that is not so expensive - and somes in small amounts. Use the flat cardboardboxes for sending paintings, and put extra protection around them when shipping.