Transcription
One of the oldest knit objects in the world is a sock, that’s about 800 years old. It was a simple thing: a pattern of knots in the shape of a cylinder, with a bend towards the end for the heel. But it was also the start of something revolutionary: a technology that could take a simple string and transform it into a useful, 3D object.
Now, perhaps knitting doesn’t fill you to the brim with excitement. I get it. But you know who is excited about knitting? Physicists. Because by decoding the patterns of stitches that create different shapes, they can figure out how to knit all kinds of complex 3D fabrics. And I’m not talking about fancy toe socks. They are designing fabrics that could transform medical bandages, soundproofing materials, and a whole lot more. And they sent us some to show you, so stick around for that.
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In the 800 years since that sock was made, knitting has spread everywhere. In fact, you’re probably wearing a knit fabric right now. T-shirts, sweaters, socks, underwear… basically anything made of a stretchy fabric is probably knitted. And making these fabrics is simple, at least in theory. All you do is create loops in a piece of string and pull one loop through the next, one row at a time. You can either pull the loop from back to front, to create a little V-shape, which is the knit stitch, or front to back to make a little bump, which is called a purl stitch. Knit and purl are the two basic stitches that make up the vast majority of all knitting. And you can mix and match the two of them to create all kinds of fun fabrics. It’s actually a little like programming, but with yarn. You have two kinds of inputs, and you can combine them in an endless number of ways to make fabrics that look and behave totally differently.
Certain patterns of stitches naturally like to curve in specific ways. And they do this consistently. For instance, if you make anything with all knit stitches on its front side, called stockinette stitch, the top and bottom will curl toward you, while the sides will curl away. But even though centuries of knitters figured out how to make all sorts of patterns through trial and error, how it all works was mostly a mystery. I mean, why do certain patterns of knits and purls create folds, zigzags, or rolls?
The answer, of course, lies in physics. Researchers have figured out that the way a fabric naturally curves has to do with a sort of “force field” created by all the knots in it. Now, normally we think of force fields in the context of things like gravity, or magnets. Like, here, all these iron filings show you the shape of the magnet’s force field — essentially, the area where the magnet’s force can be felt. And in a way, knitted yarn creates its own sort of force field. This happens because wherever two pieces of yarn cross each other, each one wants to be in the same spot. But they can’t be, so one strand gets pushed down while the other gets pushed up. And each section of the yarn naturally resists being bent and stretched around the other. So the strand that’s being pushed down reacts with a small upward force, and the strand that’s being pushed up creates a downward force. Ultimately, the yarn settles into the position where it’s under the least amount of tension. In other words, it relaxes into the lowest possible energy configuration, just like a ball coming to rest at the bottom of a driveway. That’s why, once you have made your stitches, you can stretch the fabric however you want, but the tension in the fabric will generally pull it back into its original shape. And usually, that original shape is not perfectly flat.
As you knit together patterns of knit and purl stitches, you create a field of different forces that really sculpt the fabric into different shapes. For instance, you’ve probably seen clothes with ridges like this, especially around the wrists or neckline. This is called ribbing, and it’s made with alternating columns of knit and purl stitches, which curl in opposite directions. Ribbing is best for parts of a garment that need to be really stretchy but also come back to their original shape, which is why it’s the perfect thing for necklines and sleeve cuffs. So manipulating the order of stitches and the force fields they generate is part of how you get a specific property in a garment. But knit patterns get much more complex than that. All of these fabrics, with their ridges and zigzags and bubbles, were made out of some combination of knit and purl stitches.
Now, for centuries, knitting was more of an art than a science. But then… the physicists showed up. In a 2025 study, a team of them based in Philadelphia wanted to understand how a certain knitted pattern would translate to a shape. To do that, they needed to tease apart the effects of two factors: how much the fabric stretches, and how much it bends. There’s a little bit of tug-of-war here, because that force field created by all the knots makes the fabric want to curve to reduce tension… but as soon as a fabric curves, it also begins to stretch, which creates tension. In its natural state, a fabric is balancing out these two sources of tension so that overall it’s as relaxed as possible. Logical enough — but these researchers needed a way to model all of this.
To do that, they turned to a theory that engineers use to understand how thin, curved structures, like bridges and submarines will react to the forces exerted on them. It’s called the theory of thin shells. Now, that might seem like a reach, but it turned out to be pretty useful. They used the theory to create a computer model that would predict how different knit patterns will behave, based on the different forces acting on them. And, using this model, they were able to map out a bunch of different stitch samples that would create all sorts of weird, intricate shapes. And here is a sample of some of those knit stitches. You see, like, this here. Super skinny and then you can stretch it out. That’s very cool. There’s like a wavy one here. This one is…I don’t know. I don’t know. I can’t believe this is just knitting. It looks like there’s a stitch in here, but there’s not. If you pull it tight, it’s just knits and purls. The surprising thing is that the bends in the fabric don’t always happen along the lines where you switch from knit stitches to purl. So it’s actually really hard to predict instinctively what a certain stitch pattern will end up looking like. But this model can do that.
Now that’s cool and all, but you might not want to make a sweater out of these patterns, and that’s okay because scientists have much bigger plans. We’ve been good at sweaters for a while. Honestly, what are we gonna do there? They’re already great. But by programming knitted fabrics to have specific properties, you can design sheets of material that can do basically whatever you want. One potential property of fabric that researchers are especially interested in is self-folding — a property of fabric that naturally forms ridges or creases. Now, self-folding isn’t necessarily very complex. Ribbing is actually a kind of self-folding. The columns of alternating knits and purls essentially make your sweater cuff fold back in on itself once it’s over your hand. But self-folding can do a whole lot more than keep you cozy.
One type of self-folding fabric is what’s called an auxetic fabric: When it expands in one direction, it also expands in the perpendicular direction… kind of like these toy balls. This happens because when you pull the fabric in one direction, you’re not really stretching the fabric. You’re unfolding it, almost like opening up opening up those little fortune teller paper things that we had in school. The useful thing about auxetic fabric is that different parts of it can stretch different amounts, so if you put it around something with an irregular shape… like a person or any other item, it tends to be really form-fitting. So, it could be used to make nicely fitting clothes, but it could also be used as packaging, to protect oddly-shaped objects from getting damaged. And auxetic fabrics have another big advantage that has to do with the way they absorb energy. See, when you squeeze any regular material, the part you squeeze gets thinner, and the sides bulge. Just think of what a pillow does when you plop your head onto it. But auxetic fabrics do the opposite: When you squeeze an auxetic fabric, there is no bulging out the sides. Instead, the fabric actually scrunches up in all directions. So the part you’re pressing on gets extra dense instead of thinning out. This makes auxetic fabrics really good at absorbing energy. Whenever something compresses the fabric, there’s just more material at the point of impact to help absorb that energy. That has all sorts of useful applications. I mean, to go back to the idea of using it as packaging material — something that bunches up when it’s compressed is basically reactive bubble-wrap. And researchers have also found that auxetic fabrics are really effective in soundproofing. Because the way that soundproofing materials work is by absorbing lots of invisible impacts from sound waves. Researchers have already tested out some different knit patterns to figure out what designs and materials work well for keeping the noise down. They haven’t made it into the real world yet, but they could one day replace some of the foam panels we use in this studio today.
Auxetic fabrics aren’t the only knit fabrics scientists are interested in, though. Some other researchers are eyeing this technology from the field of wearable electronics. Wearable electronics can be anything from an Apple watch to a form-fitting shirt that picks up information about your body in real time. The ones that are integrated into clothing need to be able to stretch and bend in really precise ways, and simple knit patterns could help engineers level up these designs. So, soon, knitted materials might not just be keeping us warm, but also protecting packages, absorbing noise, and helping doctors monitor their patients’ bodies. And what this all goes to show is that modern science isn’t the only way of developing sophisticated technology. Knitting evolved purely through intuition and trial and error… but those knit patterns that emerged from generations of knitters tipped off scientists that there might be something useful here. In the end, we have ancient skills and modern science working together to create something that neither could have done alone.
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