Weatherproofing Corrugated Packaging for Rainy Climates

Why Moisture Weakens Corrugated

Corrugated board gets its strength from the fluted medium glued between two flat liners. Those flutes act like a row of arches, and arches are strong until they get wet. Moisture softens the starch adhesive that holds the layers together and weakens the paper fibers, so a damp box loses much of its stacking strength.

In Seattle and the rest of western Washington, long wet seasons and humid winters make this a practical concern. Boxes kept in unheated warehouses, left on open docks, or carried in unconditioned trucks are all exposed.

Coatings and Treated Board

Wax-impregnated board has long been used where boxes meet water, such as produce and seafood. The wax resists water, but it also makes the boxes hard to recycle, because wax interferes with repulping. Newer water-resistant coatings aim to give similar protection while staying recyclable; ask your supplier what is available and how it is recycled where you are.

Wrap and Liners

Stretch-wrapping a palletized load gives it a shell against rain during dock transfers. Wrap from the base up and bring the film down over the pallet so water does not wick up from puddles. For individual shipments, a poly bag inside the box protects the contents even if the outside gets wet on a porch.

Storage and Handling

• Keep boxes off the floor on pallets or shelving.
• Store away from exterior walls in uninsulated buildings, where condensation collects.
• Keep the storage area as dry as practical; a dehumidifier can help.
• Minimize time on open docks and cover pallets during transfers.

Choosing Board for Wet Conditions

Heavier liners and double wall construction resist moisture for longer simply because there is more material. For shipments that will see damp conditions, stepping up a grade gives a margin of safety. If you are buying used boxes, check that they are dry and firm before you use them.