Corrugated cardboard gets its strength from a wavy inner layer sandwiched between flat sheets.

The longer version

A flat sheet bends easily because its material sits close to the neutral middle. Separate two flat sheets with a wavy one and you push most of the material away from that middle, which resists bending far better, while the trapped air keeps the panel light. The flutes also act as small upright columns that stop the faces collapsing together.

The idea was patented for packaging long after paper became cheap, and the same trick appears in corrugated roofing metal and in sandwich panels for vehicle floors. Stacking strength comes mostly from the vertical flutes, so a box is much stronger upright than on its side, which is why printed arrows show which way to stack it.

Where this entry sits

Odd Little Things looks at the ordinary objects people touch every day and the small mechanisms and histories hiding inside them. Buttons, zips, pencils, mirrors, stairs, stamps, packaging, and road signs all get their turn. The full list sits on the Odd Little Things page, where every entry is listed in order.