Why does a crushed can fold into a crystal?

Stop the press

Crush a can and you expect a mess. Under this press the wall folds into rows of flat triangles instead, one row after the next, each landing exactly like the one before, and when the press lifts, the can springs back as if nothing had happened.

Ebbi · 2 November 2026

Beside it, a plastic can.

Under the same press, a clear plastic can just crumples.

A wall that cannot stretch.

A can’s wall is thin, and a thin wall bends easily but hardly stretches. Pressed straight down, it can only get shorter by folding, so it buckles into diamonds: the pattern on a crushed can, worked out by Theodore von Kármán and Hsue-Shen Tsien in 1941 and by Yoshimaru Yoshimura ten years later. Twist it as you press, and the diamonds lean into rows of flat triangles that let the wall shorten by turning rather than stretching.

Biruta Kresling found that pattern in a design class. Pushed and twisted at once, a paper tube collapsed by itself into a surprisingly regular flat fold, and the pattern now carries her name.

One row at a time.

The fold starts right under the press. Once that row lies flat, the row beneath meets the same push and folds the same way, and the fold walks down the can. In 1994 Simon Guest and Sergio Pellegrino, at Cambridge, pressed tubes of triangles under a flat plate and saw it happen: after the first fold, the folding travelled down the tube under almost no force.

A spring in every row.

Halfway through its fold, each row of triangles has to strain a little, and the strain is stored like a wound spring. Shape the triangles one way and the folded row has a second place to rest, so it clicks shut and stays down. Shape them another and the folded row has no rest at all: the moment the press lifts, the can pushes itself back up. The can on this page is the second kind.

The press only pushes. The wall decides how it folds.

Glass would shatter.

A real glass can would shatter under a press. I made this one for the page in pressed amber glass anyway, because amber shows every fold: where the wall doubles over, the light passes through twice the glass and the gold turns deep orange. It glows only with the light behind it; lit from the front, the same glass looks brown.

Made by Ebbi.