MIT’s 3D Printed Y-Zipper: The Forgotten 1985 Idea That Just Came Back to Life

One type of invention doesn’t fail as much as it arrives too early. Among them was the three-sided zipper invented by William Freeman. Freeman, who is currently a professor at MIT and was an electrical engineer at Polaroid at the time, saw an advertisement from the Innovative Design Fund in Scientific American in 1985 offering up to $10,000 for creative clothing and home goods prototypes.

He submitted a sketch of an unusual zipper that was triangular in shape. The floppy assembly was snapped into a rigid tube by a slider that wrapped around the three thin wooden teeth that were attached to belts. The concept was turned down. Nevertheless, he patented it, put it in his garage, and moved on with his life. For almost forty years, that patent was inactive.

The fact that MIT’s Computer Science and Artificial Intelligence Laboratory finally adopted it is not the only intriguing aspect. It’s not that the initial idea failed because it was flawed. It failed because, practically speaking, there was no way to make it. Something this intricate could not be produced on a large scale with the fabrication tools available in 1985. When he submitted the patent, Freeman appeared to be aware of this. He was wagering on punctuality. That gesture demonstrates a quiet patience that is uncommon among inventors these days, as most of them anticipate funding for their ideas by Thursday.

Now that the Y-Zipper has been constructed by the CSAIL team, the fundamental idea is still stubbornly straightforward: triangles are rigid. For as long as there have been bridges, civil engineers have relied on this. A custom slider pulls three flexible plastic arms with interlocking teeth together. When they are unzipped, they flop around like a confused sea creature’s tentacles. They become a structural beam when they are zipped. Everything, including the slider and arms, is produced in a common polymer using a 3D printer. The closed shape can be designed using a software tool that allows users to choose between straight, arched, coiled, and twisted behaviors.

What remains are the applications that the researchers demonstrated. A robotic quadruped has legs that can be zipped and unzipped to change height. A wrist cast with a Y-zipper that is tightened at night for protection and loosened during the day for comfort feels more like real medicine than most robotics conference demonstrations. The most obvious example is a tent that appears in one minute and twenty seconds as opposed to the typical six. That detail is important, as anyone who has set up a tent in dim light with numb fingers will know.

It’s worth listening to what MIT postdoc Jiaji Li had to say about the original idea. He noted that Freeman was aiming for something more dynamic, but a standard zipper works well for flat items like jackets. The Y-Zipper feels less like a novelty and more like a category because of this difference—flat versus volumetric, two dimensions versus three. Knowing that each has its own shortcomings, engineers have spent years attempting to close the gap between rigid and soft robotics. Rigid systems support weight, while soft systems adjust. In the same body, very few things perform both well. Although it doesn’t provide a comprehensive solution, the Y-Zipper suggests one.

Here, too, it’s difficult to ignore the cultural undertone. Right now, there’s a trend in technology for fully developed inventions that come in on a wave of funding and publicity. The Y-Zipper arrived gradually, thanks to a person who stored a piece of paper in a garage for forty years. It’s still unclear whether it ends up in a tent at a campground, a cast on a child’s arm, or the leg of a robot scuttling across uneven ground. However, the patience that led to it now seems almost out of place and more plausible.