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Writer Mary Roach Reveals How to Read a Cardboard Box

Writer Mary Roach Reveals How to Read a Cardboard Box

(Editor's Note: Welcome to WildCard, where the unpredictable worlds of cardboard and imagination collide, is our newest exhibition; it opens on June 17. Mary Roach spent time with our WildCard team then made some surprising discoveries about cardboard boxes.)

People whose profession involves cardboard boxes—making, packing, and shipping things in them—don’t say “cardboard box.” That’s a layman’s term; vague and imprecise. Professionals say “corrugated fiberboard container.” Even that is imprecise. Do you mean singlewall corrugated fiberboard or doublewall? (That is, is there one layer of corrugation between two linerboards, or two between three: regular sandwich or club?) What’s its Edge Crush Test rating? Burst strength? How does it fare on the International Safe Transit Association 3A Test? With boxes, it’s all about strength. The “small parcel distribution environment” is an ungentle place.  

Most of what I know about corrugated fiberboard I learned from a three-way conversation with the United Parcel Service (UPS): me, package engineering manager Quint Marini, and spokesperson Dan McMackin. Somewhere toward the end of the call, McMackin mentioned something amazing (to me). Companies that make corrugated fiberboard boxes list the vital stats in a small circular pedigree on the bottom called the Box Certificate. What I find amazing is that dozens upon dozens of corrugated fiberboard containers have come and gone from the end-point distribution environment known as my life and not once have I noticed this little coded box tattoo, this visa stamp for a secret cardboard nation.

As soon as we all hung up, I left my office and went out into the streets of downtown Oakland. Within minutes, I found an empty box on the sidewalk. I flipped it over. Voila! 

The outer ring tells the box’s provenance; in this case, WestRock in Murfreesboro, Tennessee. Then comes the construction: singlewall is just fine for airy confections and other light items. ECT is the Edge Crush Test score. Gross Weight Limit is less straightforward than it sounds, but helpful in a general way. If, say, you’re scrounging used boxes for a move, you’ll want to pass over a singlewall donut box with a gross weight limit of 85 pounds, for example, and snatch the doublewall gross weight 95 down the block that was used to ship bags of rice. (Triplewall exists, but don’t look for it outside bakeries and produce stores. It’s used for big heavies such as air conditioners and transmissions.)

UPS discourages you from shipping your breakables in any kind of scrounged box. Like people, cardboard becomes “fatigued” after a lengthy journey. Even if it looks pristine, a used box has lost as much as half its strength. Another similarity between people and cardboard: Humidity wipes them out. In 90 percent humidity cardboard’s strength is lowered by 60  percent. And, finally, cardboard, like humans, gets weaker with age. After 180 days in storage, a box loses 48 percent of its strength. 

The ultimate in corrugation, Marini said, is Hexacomb (made by the Packaging Corporation of America not by UPS). Rather than employing the strength principles of simple triangles, arches, and columns, as standard corrugation does, Hexacomb is configured like honeycomb. You see it used for package inserts, like those bumpers fitted over the sharp corners of heavy items: a computer mainframe, say, or a file cabinet. The PCA motto is “We do the hard to do,” and its website provides examples: eggs, live crickets, ten-gallon aquariums, and the strange, Goldilocks-ian “three different-sized urinals in a single shipping container.”

Not to be outdone, McMackin told me about a special box UPS designed for shipping bees. It has a pheromone-saturated disc at its center to draw the bees away from the sides and corners, where they’re more likely to be jarred and injured. Early iterations overdid the pheromone, and wild bees took note of passing UPS trucks. McMackin recalls some of the calls that came in: “I don’t know what’s going on, but every bee in Jones County is following my truck.” 


Welcome to WildCard runs from June 17 to September 4, 2017.