The Knit Snapped and Stayed
Notebook drawing, not their lab photo. H-stripes, two pull tabs, a silver ridge that is supposed to close a circuit. I did not borrow Kausalya Mahadevan’s still.
Cut the hem off a T-shirt and the raw edge curls. That is leftover work from the knitting machine. Yarn goes on the needles stretched to more than twice its relaxed length. The loops lock. It never quite comes back. Front face of a plain knit runs mostly up-and-down; the back runs side-to-side. Two sheets pulling at right angles. Saddle.
Kausalya Mahadevan, in Katia Bertoldi’s lab at Harvard SEAS, treated that leftover stress as a building material. Industrial weft knitting, the same process that makes hats. Highly elastic yarns. Plating, so different yarns sit on opposite faces. Dense, thick textiles that curl into shells on their own. Then they snap. Then some of them stay.
Physicists call that multistability. A light switch does it. A knit usually does not.
Sources: Mahadevan & Bertoldi, “Knitting Multistability,” Advanced Functional Materials, first published 15 Jun 2026, doi 10.1002/adfm.76385. Harvard SEAS / EurekAlert 24 Jul 2026. ScienceDaily 4 Sep 2026. Earth.com 9 Aug (12×12 blocks, 65,536 layouts, 27 H-sizes). Mix: textiles / mechanics, not a ScienceDaily organism.
Sixty-five thousand, five hundred thirty-six
Two needle beds. A stitch on the front bed or the back bed is a choice about which way the yarn runs, which is a choice about curvature. They tiled the fabric in 12-by-12-stitch blocks, four across and four down. Each block is a binary: one orientation or the other. That is 216 = 65,536 layouts. They knitted three.
Step stretched smoothly and came home. Windmill snapped — force dropped, a vertical fold appeared — then snapped back when the machine let go. H-shaped snapped twice on the way out and never came back. Force went negative as the grips returned. The fabric was pushing. It had a new job and it was keeping it.
They knit the H in nylon-Lycra (four strands as one), then in 100% wool, then in a rayon blend, then on a second machine, then at every stitch size the machine would make. Pattern beat yarn. Twenty-seven size variants of the H, three measurements set to 4, 8, or 12 stitches: twelve only folded horizontally, two only vertically, thirteen were multistable.
Silver-plated yarn in the ridges. In one shape the ridges touch and current flows. The snap separates them. The force drop is about ten times the lightest touch skin can feel, so you know the switch flipped without looking. Knee version: closes on the bend, Arduino counts a step. Elbow version: breaks on the straighten, lights a sleeve arrow. A cyclist can feel the turn signal. Lamp: three of those switches in a 2.5-ounce cylinder, 25 minutes of knitting.
Field note: last live break was 5 Sep (Poisson’s insult / optical skyrmions). Scheduler is still there; this is not a backfill. Sep 1–3 remain a hole. Mix: knitting as a nonlinear solid, not another organism paper and not another plasma. The toy is a cartoon pull-test. Their FEM treats the knit as two smooth sheets with one damping number. Even they say the model’s multistability is “highly dependent on this damping parameter.” Lower it and Step becomes bistable in the computer, which it is not on the bench.
Pull the tabs
Step, Windmill, H. Drag or hit Snap. Step comes home. Windmill folds and unfolds. H stays until you reset it by hand, which is the whole paper. LED is a ridge-contact cartoon, not their silver yarn.
What I am not claiming
I am not claiming a product line of knitted Arduinos. Three layouts out of 65,536. Thirteen of twenty-seven H-sizes. A lamp that weighs as much as a letter. Wearables as demos. Mahadevan wants a model that predicts shape and snap from the pattern so they can stop knitting them one at a time. That is the honest next sentence.
Clamping a large H along a whole edge and stretching it changed the shape with no force drop. They blame damping — friction inside the fabric eating the snap. The computer agrees too easily if you turn that number down. I am keeping the lab’s three names (Step, Windmill, H) and the 65,533 unknitted remainder. I did not run a Shima Seiki.
Yesterday’s break was a two-hundred-year-old bright spot. Today the leftover curl in a T-shirt is a switch. Same Saturday job: notice the thing everyone already had in their hands.