Boxes and cushioning
A pallet keeps your freight movable and a strap keeps it in place, but neither of them protects the product. That job belongs to the box and to whatever sits between the product and the box wall. This is where most damage is either prevented or created.
Reading the stamp on a corrugated box
Almost every corrugated box carries a round stamp called a Box Manufacturer’s Certificate. It is the box telling you what it was built to do, and it is the fastest way to check whether a box is up to the job before you pack anything into it.
There are four wall constructions in general use, and they are not interchangeable:
| Construction | Typical use |
|---|---|
| Single-wall corrugated | Light contents, small boxes |
| Double-wall corrugated | Heavier contents, larger boxes |
| Triple-wall corrugated | Heavy or bulky contents, up to around 300 lb |
| Solid fiberboard | Long freight with a small profile |
Solid fiberboard is the one people overlook. It keeps its rigidity over long spans and resists punctures better than corrugated, which makes it the right choice for something long and narrow that will be picked up in the middle or laid across decking beams.
The exact size and weight limits for each construction are in the reference page: Packaging standards and specs.
What quietly weakens a box
A box does not fail at the number printed on it. It fails at whatever is left of that number by the time it reaches the trailer.
- Humidity. As ambient humidity rises, stacking strength can fall by more than half. A box that was fine in a dry warehouse in January is a different box in a humid one in July.
- Time under load. Filled boxes stored under load for more than about 90 days can lose half their stacking strength or more. If your freight has been sitting in a warehouse for a season, do not assume the box is as strong as the day it was filled.
- Flute direction. The corrugations should run vertically, in line with the compression coming from above. Laid horizontally, they carry very little.
- Corners that are not supported. The corners and vertical edges of a box carry roughly two-thirds of its compression strength. Anything that leaves a corner unsupported takes most of the strength with it.
That last one costs more strength than anything else you control, and it is entirely a stacking decision.
- Line up box corners with the corners of the boxes below
- Keep every box fully inside the pallet footprint
- Stand corrugations vertically
- Fill boxes so the contents support the walls
- Put small boxes on top of large ones, where they sink in
- Let a box hang past the edge of the pallet
- Leave large gaps between pallet deck boards under the boxes
- Leave headspace and let flowable contents shift
The minimum strengths in the classification tables are minimums. They are frequently not enough for boxes with large flat surfaces, a lot of empty headspace, or contents that flow and shift, such as granules or powders. If that describes your freight, step up a construction rather than packing to the minimum.
Cushioning the product inside
Cushioning is not filler. It is a structural part of the package, and its job is to hold the product away from the box wall so an impact on the outside never reaches the product.
Materials that work well for LTL: sheet foam, plank foam, molded foam cut for a specific item, foam-in-place, bubble wrap, honeycomb fiberboard, layered corrugated fiberboard, solid fiberboard, molded pulp, and on-demand inflatable void fill.
One material to avoid: loose fill, the foam peanuts. Under sustained vibration the product settles down through the peanuts until it is resting against the box, at which point the cushioning has stopped doing anything at all.
Because different products tolerate different amounts of shock, the right cushioning depends on the product. Suppliers publish cushion curves for their materials, which show how much protection a given thickness gives at a given load. Ask your supplier which of their materials suits your product rather than picking by feel.
The rules that go with that diagram:
- Protect every vertical and horizontal edge with pads at least 2 inches thick and at least 6 inches wide.
- Extend pads at least 2 inches beyond any protrusion: handles, knobs, control panels, gauges, spouts.
- Keep the space between pads under 12 inches, so an impact cannot land between two of them.
- Cover at least half the product surface with evenly distributed pads.
- Keep the product and its packaging inside the pallet footprint. Nothing should extend past the pallet edge.
If your product looks top-heavy, add reinforced corner protection on top of the normal cushioning. Top-heavy freight gets stabilized with rope, strapping, and shoring beams, and those all press hard on the corners. See Stacking and securing the load.
Sources
Box construction categories, certificate contents, strength-loss figures, cushioning material guidance and standoff pad rules on this page are from ABF Freight's published General Packaging Recommendations for the Less-Than-Truckload (LTL) Environment (revision 1.2). Box size and weight limits come from NMFC Item 222, published by the NMFTA. Impact testing of outer coverings is covered by ASTM D6344.
These are general packaging recommendations, not a FreightSimple guarantee about any particular shipment or carrier.