Short answer: Corrugated absorbs moisture from humid air, and wetter board is weaker board. Industry testing commonly shows boxes stored at very high humidity can lose roughly half of their stacking strength. In Florida, spec boxes for real-world conditions, not lab conditions.
Why humidity matters so much here
Box strength ratings like ECT are measured under standard lab conditions of about 50% relative humidity. Tampa Bay's humidity is often well above that, especially overnight, in summer and in warehouses without climate control. Corrugated is made of paper fibers that absorb moisture, and as the board's moisture content rises, its compression strength drops.
Humidity combines with other strength-killers that are common in real warehouses:
- Time under load. Boxes slowly lose strength the longer they're stacked (called "creep"), and humidity speeds this up.
- Pallet overhang. Boxes hanging over the pallet edge lose support at their strongest point, the corners.
- Interlocked stacking. Brick-pattern stacking helps stability but reduces compression strength compared with column stacking.
- Temperature swings. Moving between cold storage and Florida heat causes condensation on the board.
How to spec boxes that hold up in Florida
- Build in a humidity safety factor. Calculate the required stacking strength for your load, then add margin for humidity and storage time.
- Spec by ECT. ECT predicts stacking strength better than burst strength, and helps you add strength where it matters without over-building.
- Use moisture-resistant board where needed. Coated and moisture-resistant boards help with cold chain, produce and long-term storage.
- Fix the pallet pattern. Eliminate overhang and column-stack heavy loads where stability allows.
- Shorten storage time. Smaller, more frequent box deliveries keep fresh, dry board on your floor.
- Store boxes off the floor and away from dock doors. Unused flat boxes absorb moisture too.
- Match the tape to the conditions. Choose adhesives that hold in heat and humidity. See our packaging tape guide.
Getting it right
The goal isn't the strongest box. It's the right box: strong enough for your real Florida conditions without paying for board you don't need. If you're seeing crushed cases or leaning pallets, send us your box specs and a few photos. We'll review your setup as part of a free packaging audit.