Paper, Plastic, or Steel?

The ancient Chinese art of paper folding is probably not in most people's minds when rushing to bag their groceries. But engineers have now built a foldable grocery bag from steel (go ahead, load it with soda bottles!) using an origami-inspired design that could help speed up factory packaging processes. The technique may eventually lead to buildings that can change shape at the push of button.

"Origami engineers" build a variety of objects by folding sheets of rigid material along set creases. In the past, they have used the technique to create foldable solar panels, for use in space, that can be quickly and easily packed into a small volume for transport in shuttles. Now, origami engineers Zhong You and Weina Wu of the University of Oxford in the United Kingdom have tackled a more down-to-earth problem: whether a tall shopping bag built from a rigid material or an open-topped cardboard box could ever be folded flat like a traditional grocery bag without having to open its bottom.

The question is important in the packaging industry where, currently, cardboard boxes can only be flat packed if both their top and their base are left open, You explains. "If you have moved house, you know how much time is wasted constructing the base of the box before you can put anything in it, and it's even worse on a factory assembly line," he says. "Making cardboard boxes that can be folded flat, even with their base in place, will speed up automated packaging in factories."

In 2004, mathematician Erik Demaine of the Massachusetts Institute of Technology in Cambridge and his colleagues proposed a theoretical pattern of origami creases that could be set into a tall bag made from something more rigid than paper and allow the bag to be folded flat. The bag could never be made in practice, however, because it required infinitely thin material. Now You and Wu have come up with an alternative crease pattern, which adds a number of extra creases to the traditional pattern used in conventional paper grocery bags. They successfully constructed a prototype of a bag made from a number of stainless steel plates, stuck on to a light, flexible plastic sheet. The edges where the plates meet serve as "creases," along which the bag can be bent. The steel bag can be collapsed down as flat as a standard paper grocery bag (see picture). "We used steel because if it works for that, it will work for less-rigid materials," You says. The pair are now discussing their design—published online today in the Proceedings of the Royal Society A—with carton manufacturers.

"They've built a cool working model, so this is definitely practical for the packaging industry," Demaine says. He would now like You and colleagues to investigate whether other bags with different heights and widths can be folded flat. The ultimate dream for origami engineers is to make buildings from rigid materials that can be reconfigured according to need, Demaine says. If researchers can realize that ambition, then someday your kitchen may have counters that fold away and you may even be able to fold up your television, he says: "That's a long way off, but looking at rigid shopping bags is a good step toward that."

Check out a video of origami that folds itself.