Warehouse tests miss the humidity
A 20-inch party box passes a dry stack test without trouble. The failure appears only after the box crosses a humid climate, where the board absorbs moisture and loses up to a third of its stiffness.
The board matters more than the size
For party sizes you need board chosen for the route, not just the pizza. BC double wall with a raised rim holds the stack, but only if the board is specified with the destination humidity in mind.
What we change for Gulf shipments
We switch to a stiffer double-wall grade, add a moisture-resistant treatment to the base, and raise the rim so the top never touches the cheese. The box costs more, but it arrives as a box and not a pancake.