Where does corrugated cardboard get its strength?

When you’re eating a thin crust pizza, how do you hold a slice in your hands?

If you hold the crust flat, the slice will droop and the toppings will fall off. So you fold the slice and the crust forms a curve in your hand. This is pretty basic Pizza Eating 101.

But what does this have to do with corrugated cardboard?

Also, why do we at Packsize insist on always calling it corrugated cardboard?

Let’s investigate.

Some math and pizza

So the reason the pizza keeps its toppings when you fold it is due to a theorem called Gaussian curvature. this theorem has one of the least understandable Wikipedia pages ever, so I’ll try to explain it here in layman’s terms.

Take a look at the picture below and try to imagine wrapping each of the objects in a sheet of paper without folding, creasing, or ripping the paper.

You could really only successfully wrap the cylinder, right? The other two objects would require some creative origami to be successfully wrapped.

A flat sheet of paper has a Gaussian curvature of zero. Wrap it around the cylinder, and it would still be zero—even though you have transformed it. But if you try to wrap it around the other two objects, the curvature would have to change. The object on the left has a negative Gaussian curvature, while the sphere on the right has a positive Gaussian curvature.

When you “fold” your slice of pizza to eat it, you have transformed it, but you have not changed its Gaussian curvature. The pizza can no longer flop forward and drop your toppings without crumpling.

The same principle works with a sheet of paper. If the sheet is curved length-wise, it can not bend width-wise without creasing.

Back to (corrugated) cardboard

So why do we always call it “corrugated cardboard”? The term “corrugated” means “to draw or bend into folds or alternate furrows and ridges.” If you view the edge (cut-side) of a piece of corrugated cardboard, you’ll see a wavy texture.  You’ll see the term also used with corrugated metal, a favorite texture in dystopian future settings.

“Nothing protects you from radiation quite like rusty metal!”

The wavy corrugated medium prevents the metal and fiberboard from folding in the same way that bending a slice of pizza prevents it from collapsing. So most people in the industry like to use the term corrugated cardboard, because to them, “cardboard” is referring to basic card stock.

And now an experiment

Let’s try making our own corrugated cardboard model. I took a sheet of paper, folded it into a fan, and then stuck it between two sheets of paper. The model corrugated cardboard clearly wasn’t as floppy as a regular sheet of paper, but could it hold any weight?

It can!

There are some other factors that make the corrugated stronger:

• The weight of the liner (liner meaning the sheets that sandwich the corrugated)
• The width of the corrugated folds
• The strength of the adhesive holding the corrugate together

But Gaussian curvature is what makes corrugated cardboard possible. Without it, we might as well be using extra thick wrapping paper.

We did a blog post that explained how to understand how strong corrugated is just by reading the name. Read it by clicking here.

Packsize is a leader in the world of corrugated cardboard, which we sell in the form of z-Fold^®. If you’d like to learn more about what we can do for your business, fill out the form below to download our white paper: “What can On Demand Packaging^® Do for You?”