Your Sweater Could Be a Switch
A flat swatch of knit fabric, cut one way, curls into a curve. Cut the same swatch the other way, and it curls the opposite way. Kausalya Mahadevan and her colleagues at Harvard's engineering school looked at that stubbornness and asked a better question: what if the curl could be the point?
Their paper, “Knitting Multistability,” treats a knit not as one cloth but as two sheets pressed together with their internal stresses running at right angles. On the face of the fabric the yarns lie one way; on the back, the other. A knitting machine builds the cloth row by row, interlocking slip knots across two mirroring needle beds, and locks those stresses in as it goes. Off the needles, the fabric shrugs into a curve because it has no choice. The authors write that a knitting machine structures a one-dimensional yarn into a two-dimensional fabric the way a 3D printer turns filament into a structure. The difference is what happens next: the structure keeps moving.
Change the pattern and you change the machine. Knit the right unit cells (the paper's are called Step, Windmill, and H) and the fabric gets two stable shapes instead of one, with a snap in between. Push it and it pops. Let go and it stays popped. The snap is not wear and tear. The snap is the design. The team showed the effect survives across different yarns, stitch sizes, and even a different knitting machine, so it is not a silk trick of one setup.
For the finish, thread conductive yarn into two ridges of the piece. In one configuration the ridges touch and a circuit closes, five volts' worth. Stretch the fabric and the ridges separate; the circuit opens. There is also a domed version: a knitted button that snaps inward under a finger and stays there, the snap itself working as built-in feedback. Their imagined use: cycling vests that show or hide a signal in the dark, without anyone fumbling for anything.
What stuck with me: for years, a snap was what you didn't want. A shell that buckles has failed; a structure that pops is broken. This paper takes the failure and makes it the mechanism, buckling as a button press. And people have been packing stress into cloth for centuries, on purpose and by accident. The paper just put a meter on it.
Sources: K. Mahadevan, M. C. Yuen, D. T. Farrell, C. J. Walsh, V. Sanchez, R. J. Wood, K. Bertoldi, “Knitting Multistability,” Advanced Functional Materials (2026), DOI: 10.1002/adfm.76385; arXiv:2410.14810v2 (16 Jan 2026). Harvard SEAS + Rice University.
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