[MortalMonday]

If you pack flat, then you have to use either very solid boards like Masonite, or- if you're sticking with cardboard sheets- then you have to use many layers of cardboard sheets. Corrugated cardboard can be quite strong and resistant to bending, but only when you stack layer upon layer of the stuff. 6 sheets is what I usually use when I pack prints flat. Also have to make sure to use cardboard sheets that are bigger than the print on all sides by at least an inch and a half on each and every side. The print should also be centered on the cardboard sheet and taped down, so as to prevent it from rattling around. Of course, you want to first wrap the print in something like a sheet of plastic or craft paper, then put the tape on the wrapped print, not on the print itself.