From soft to rigid: Y-zipper enables change in object stiffness
MIT has refined an approximately 40-year-old technique to transform flexible objects into a rigid state. The Y-zipper comes from the 3D printer.
The Y-zipper solves an annoying problem when setting up a tent: the tent poles are simply zipped.
(Image: Jiaji Li /Screenshot)
Researchers at the MIT Computer Science and Artificial Intelligence Laboratory (CSAIL) have revived an approximately 40-year-old technique of a triangularly arranged zipper to create objects with variable stiffness. The application scenarios are diverse, ranging from camping equipment to medical applications, robots, and art installations.
In 1985, the Innovative Design Fund sought innovative ideas in the fields of clothing, home textiles, and home accessories in Scientific American. $10,000 was offered for a working prototype at the time. William Freeman, a young engineer then working at Polaroid, entered the competition with his newly invented triangularly arranged zipper. The zipper allows three narrow wooden strips to be connected triangularly using a slider over straps. He wanted to transform chairs, tents, and bags from a soft to a rigid state, making them easier to pack and assemble. Freeman did not win the prize, but he patented his invention without putting it into practice.
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Freeman is now a professor at MIT and revisited the old project of developing objects with adjustable stiffness to refine them with new techniques. The result is a triangular Y-zipper that can be designed using design software according to the desired stiffness and shape and printed using a 3D printer, as the MIT scientists write in the study “Y-zipper: 3D Printing Flexible–Rigid Transition Mechanism for Rapid and Reversible Assembly”, which was published in the Proceedings of the 2026 CHI Conference on Human Factors in Computing Systems.
The principle of the Y-zipper is not particularly complicated: Three chains of specially shaped plastic links are connected via a triangular slider. In the unconnected state, the chains are flexible; in the connected state, depending on the design of the chain links, they assume a more or less rigid state. In addition to stiffness, scientists can also determine the shape in the rigid state using the design software – for example, whether it should be straight, curved, spiral, or twisted.
Tent poles, flexible bandages, robots, and art installations
This gives the Y-zipper a wide range of applications. For example, the researchers developed “tent poles” that can be stored compactly in their open, flexible state and then zipped into a rigid form to support a tent.
The scientists also see potential in the field of adjustable wearables, for example, for medical applications. To demonstrate this, they placed a custom-curved Y-zipper around a wrist brace for wrist fractures. By tightening the zipper, the brace can be loosened or tightened. This allows the patient to adjust it within medical limits for their comfort.
It is also possible to automate the zipping process of a Y-zipper using electric motors. This can be used to create robot legs, for example, that can be automatically adjusted in length. The robot can decide for itself, depending on the terrain, what leg length is necessary to overcome it without problems.
The researchers also demonstrated the artistic potential of the Y-zipper technology with a winding artificial flower: driven by a static electric motor, the flower straightened up and “bloomed.”
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On the other hand, there is little to worry about regarding the durability of the technology, according to the study. Researchers from the MIT conducted a series of durability tests. They used PLA and TPU for 3D printing the zippers. PLA proved to be more resistant, TPU more flexible. The researchers repeatedly opened and closed a Y-zipper over a longer period using an electric motor actuator. Fatigue symptoms only appeared after approximately 18,000 open and close cycles. The scientists see the secret to the long durability in the fact that the stress is absorbed by the elastic structure.
(olb)
