Welcome back to My Weird Prompts. I’m Corn Poppleberry, here with my brother Herman. Today we are delving into a piece of everyday engineering that literally holds our lives together. We’re talking about the zip, or the zipper, that little track of teeth on your jacket, your jeans, your luggage. And we are incredibly fortunate this week. Given the, well, the budget environment this year, we honestly did not think we could book someone of her calibre. But she cleared her schedule, and we are so grateful. Mindy Robinson is a researcher, a thinker, a person who has agreed to be here, and today she is our expert on fasteners. Mindy, welcome to the show.
Mindy: Thank you, Corn. The studio is a little cold today. I can feel it on my ankles.
Mindy, it is a genuine pleasure. I have to say, I’ve been looking at zips my whole life and I realise I have no idea what’s actually happening in there. I’m so glad we have a real expert to walk us through it.
To start us off at the foundation, Mindy, what is a zip?
Mindy: A zip is a fastener. It’s a thing you use to close two sides of fabric together. You pull a little metal or plastic piece, which is the slider, and that brings the two rows of teeth into contact, and they hold. So that is what a zip is.
It’s a fastener.
Mindy: It’s a fastener that works by fastening. The two sides are separate, and then you zip it, and they are not separate anymore. That’s the core function. It keeps things closed, or sometimes open, if you zip it downwards. But mostly closed.
Right, of course. So we’ve all felt that sensation of pulling the slider. But I’m curious about the initial engagement. When you start, you have to push the pin into the box, don’t you? What is actually happening in that first second?
Mindy: In that first second, you are aligning the two sides. You take the little metal pin, and you push it into the box on the other side, which is the retainer box. That makes sure the two rows of teeth are perfectly lined up. If you don’t do that, the zip won’t work. You’ll just be pulling a slider up and down and nothing will close. Which is a metaphor for a lot of effort, really.
The alignment is key. I never thought of it as a box and pin system. That’s a great way to put it. So once it’s aligned, you pull the slider up. What is the slider doing to the teeth?
Mindy: The slider is the part that does the work. It’s shaped like a Y on the inside. As you pull it up, the two rows of teeth enter the top of the Y, and the slider forces them together, and they interlock. Then at the bottom, if you’re unzipping, the Y splits them apart again. So it’s a merging and a splitting tool. It’s a very tidy little device.
It’s a merging tool. That’s a nice phrase. But I want to zoom in on the interlocking itself. Mechanically, what is the geometry that lets the teeth hold? Because they don’t just touch, they grip. Is it a hook shape, a friction fit?
Mindy: They grip because they are shaped to grip. Each tooth has a little bump and a little hollow. The bump on one tooth fits into the hollow on the tooth opposite it. When the slider pushes them together, the bumps go into the hollows, and they stay there. That’s the geometry. It’s a bump and hollow geometry.
Okay, so a bump and a hollow. That makes sense on the surface. But when I look very closely at a tooth, it seems like the bump might be on the top of one and the bottom of the next. Is it a symmetrical interlock, or is one side always the active gripper?
Mindy: I think it’s a mutual grip. They both grip each other. It’s a reciprocal relationship. One tooth can’t grip without the other gripping back. So it’s a kind of mutual dependency. Which is nice, in a way. Most things don’t have that.
That’s quite a profound way to look at a zip. A system of mutual dependency. Mindy, this is exactly the kind of insight we were hoping for. So the slider forces this mutual grip. But what keeps the slider itself on the track? It doesn’t just fall off.
Mindy: No, it doesn’t fall off. It’s held on by the teeth themselves. The slider is wrapped around the teeth. It has little channels on the sides that the teeth ride inside of. So the slider is trapped on the chain of teeth. It can’t come off unless you pull it past the end, which is why zips have stops. Little metal or plastic bits at the top and bottom that are too big for the slider to pass over. So the slider is a prisoner of the teeth it serves. It’s a bit bleak when you think about it. It spends its whole life on that one track.
That is a rather grim image. A prisoner of the teeth. But I’m still trying to picture the internal channels. You say the slider is wrapped around the teeth. Does that mean the slider is actually shaped like a tiny tunnel that forces the teeth into that bump-and-hollow position?
Mindy: Yes, it’s a tiny tunnel. A tiny, Y-shaped tunnel. The arms of the Y are the tunnels that guide the separated teeth, and the stem of the Y is the tunnel that squeezes them together. It’s a very confined space. The teeth don’t really have a choice in the matter. They just follow the path they’re given.
The teeth don’t have a choice. You’re making the zip sound like a very deterministic piece of engineering.
Mindy: It’s a completely deterministic system. You pull, it closes. Until one day the teeth misalign, or a bit of fabric gets caught, and then the whole thing jams. And at that point, you’re usually in a hurry, and you pull harder, and you make it worse. And eventually you just leave the jacket half-zipped forever. Or you throw it away. That’s the end state of most zips.
I suppose that’s true of many things. But let’s stay with the mechanism before we get to the entropy. Mindy, you mentioned the teeth are shaped with bumps and hollows. Are the teeth on a standard nylon coil zip shaped differently from the teeth on a metal zip? I’ve noticed the nylon ones feel smoother.
Mindy: They do feel smoother. The nylon ones are made of a continuous spiral of nylon filament. It’s wound into a coil. So the teeth aren’t individual pieces, they’re loops of a single thread. The metal ones are individual little metal pieces that are clamped onto the fabric tape. So the nylon zip is more of a single, flowing entity. The metal zip is a collection of individuals forced to work together. They’re both doing the same job, but the nylon one does it more quietly.
A single flowing entity. I like that. So the nylon coil is essentially one long piece of plastic that’s been cleverly shaped?
Mindy: It’s a monofilament. That means one filament. It’s wound into a spiral and then stitched onto the tape. It’s a very efficient way to make a lot of teeth very quickly. You just keep winding. It’s a bit like a spring that’s been told to be a fastener instead of a spring.
That’s a fascinating detail. So if it’s a monofilament, what is that filament actually made of? Is it nylon, as the name suggests, or is it a different polymer?
Mindy: It’s nylon. That’s why it’s called a nylon zip. Nylon is a type of plastic that was invented in the 1800s, I believe, and it’s very strong and flexible. So it’s perfect for making a coil that has to bend thousands of times without breaking.
Actually, Mindy, I think nylon was invented in the 1930s, not the 1800s. Wallace Carothers at DuPont, 1935.
Mindy: That’s later than I thought. But still, it’s very strong.
It is very strong. And it’s a material that really changed the world of fasteners. Now, you mentioned the tape that the teeth are attached to. That’s the fabric bit we sew into the garment. What’s the history there? Where did the zip actually come from? Was it always a garment thing?
Mindy: The zip has a history. It wasn’t always for garments. I was looking at this on the way here. I skimmed the Wikipedia article, actually, because I wanted to make sure I had the dates right. But I still got the nylon date wrong. Anyway, the zip was originally invented for shoes. There was a man named Whitcomb Judson who made a thing called a clasp locker for boots in the 1890s. It was a series of hooks and eyes that you pulled closed with a slider. It wasn’t very good. It kept popping open. Which must have been very annoying if you were trying to walk somewhere.
The clasp locker. I’ve seen pictures of those early patents. It looks almost like a precursor to the zip but with a completely different tooth shape. What was the breakthrough that gave us the modern interlocking scoop?
Mindy: The breakthrough was a man named Gideon Sundback. He was an engineer. He realised that if you made the teeth with a little dimple on one side and a little bump on the other, they would lock together much more securely. He made the first really modern zip in, I think, 1913. Somewhere around there. He also invented the machine that could make the teeth and attach them to the tape in one process. Before that, it was all done by hand, which was very slow. He made it fast.
Sundback is the real father of the zip as we know it. The dimple and the bump. It always comes back to the dimple and the bump.
Mindy: He called it the separable fastener. The name zipper came later. It was a brand name, I think, for a zip on a pair of boots. Goodrich company used them on galoshes and they made a zipping sound, so they called it the Zipper. And the name just stuck. Now we call all of them zippers, even the ones that don’t make a sound. It’s a bit of a misnomer. Most of the zips I own are completely silent. They just glide. The silent zipper. That’s a sad name, in a way. A thing named for a sound it no longer makes.
A silent zipper. You’re right, that is a little melancholy. But it’s a great piece of branding history. Now, you mentioned Sundback’s machine. That seems like a huge part of the story. The invention of the zip is almost the invention of the machine that makes the zip. Can you tell us a bit more about that manufacturing process? How do you actually get those tiny metal scoops onto the tape?
Mindy: You get them on with a very precise machine. It clamps each little metal piece onto the edge of the tape. The tape is woven with a thick bead on the edge, and the metal scoop is crimped around that bead. It’s a crimping process. The machine does it very fast, one after the other. I don’t know the exact speed, but it’s a lot of scoops per minute. It’s a very loud process, I imagine. A lot of clanking.
A lot of clanking. And that’s for the metal zip. What about the nylon coil? How do they attach that?
Mindy: The nylon coil is stitched on. A big needle just sews the spiral onto the tape. It’s a sewing process, not a crimping process. It’s probably quieter. More of a whirring sound. I haven’t been to a zip factory. I’m not totally sure on the exact acoustic profile of zip manufacturing.
That’s fine. We can imagine the whirring. But I’m curious about the tape itself. It’s a very specific kind of tape, isn’t it? It has to be dimensionally stable so the teeth stay aligned. What kind of weave are we talking about?
Mindy: It’s a tight weave. Usually cotton or polyester. It has to be strong and it can’t stretch. If the tape stretched, the teeth would misalign and the zip would fail. So it’s a very stable fabric. It’s probably the most stable part of the whole garment, really. The zip tape will outlast the jacket it’s sewn into. Everything around it will wear away, but the tape will remain, still holding its little teeth. A little skeleton of a fastener.
A little skeleton. Mindy, you have a real gift for imagery. So the zip outlasts the garment. That’s actually a practical point. When a zip fails, what’s the most common failure mode? Is it the tape, the teeth, the slider?
Mindy: The most common failure is probably the slider. It can become loose. It doesn’t squeeze the teeth together tightly enough anymore, so they don’t lock. Or the teeth can get bent out of shape. On a metal zip, one tooth gets pushed out of alignment, and then the whole thing stops working. On a nylon zip, the coil can pull away from the tape if the stitching comes undone. That’s a very sad failure. The coil just sort of peels off, and you can’t fix it. You just have to let it go.
Let it go. That’s the bleakness creeping in again. But before we get to the letting go, I want to push a little deeper on the geometry one more time. You’ve mentioned the dimple and the bump. I’m still trying to visualise the exact cross-section. When the teeth are interlocked, is there a tiny gap between them, or are they in full surface contact? What prevents them from just sliding apart laterally?
Mindy: They are in full surface contact. The bump of one tooth sits fully inside the hollow of the tooth above and below it. That’s what prevents lateral movement. They’re locked in three dimensions. They can’t slide apart because the bump is trapped. It’s a very complete little prison for each tooth. They’re all holding each other captive. It’s a chain of mutual captivity.
A chain of mutual captivity. That’s the second time you’ve used a prison metaphor for the zip. Do you see the zip as a fundamentally oppressive piece of technology?
Mindy: I don’t know if it’s oppressive. It’s just a bit sad. All those little teeth locked together, unable to move, just holding on until the slider comes and forces them apart again. And then they just sit there, separated, waiting to be locked back up. It’s a cycle of confinement and release that never really ends. Until, as I said, the landfill.
Let’s step back from the existential side for a moment. I want to ask about a very specific application. The airtight zip. Like on a drysuit or a hazmat suit. How does a zip become airtight? That seems to violate the whole idea of a zip having tiny gaps.
Mindy: An airtight zip has a special coating. It’s usually a rubber or plastic layer on the tape that covers the teeth. When you zip it closed, the teeth interlock, and then the rubber layers press together and form a seal. So the teeth are doing the mechanical holding, and the rubber is doing the sealing. It’s two systems in one. I’m not totally sure on that part. I’ve never actually seen one in person. I imagine they’re very stiff to operate. You’d have to pull quite hard. And if the seal fails, you might not notice until it’s too late. That’s a bit of a design flaw, really. A failure you can’t see.
A failure you can’t see. That is a bit ominous. But it’s a clever piece of engineering, combining the holding and the sealing. Now, we’ve talked about the history a bit. Sundback, the clasp locker. Was there a moment when the zip really broke through into fashion? I feel like it was a slow burn.
Mindy: It was a slow burn. It was used in boots and tobacco pouches for a long time. Then in the 1930s, children’s clothing started using zips because they were easier for kids to do up than buttons. That was a big selling point. Teaching a child to use a zip is easier than teaching them to do buttons. So zips became associated with ease and modernity. Then they went into men’s trousers. The fly zip. That was a big moment. I don’t remember the exact year. Somewhere in the 1930s as well, I think. It was advertised as a way to avoid what they called gaposis. The gap in a button fly. So the zip solved gaposis. Which is a word we don’t use anymore.
That’s a wonderful piece of forgotten vocabulary. The fear of the gap. So the zip was marketed on security and modesty, in a way.
Mindy: Security and modesty. You could zip up much faster than you could button. So it was a time-saving device. It saved maybe three or four seconds per dressing event. Over a lifetime, that probably adds up to several hours. Hours that you then spend doing other things. Like thinking about zips.
Like thinking about zips. We’ve come full circle. Mindy, I have to say, this has been genuinely illuminating. You’ve given us a real insight into the world of the zip. The bump and the hollow, the mutual captivity, the silent zipper. I feel like I understand the fastener world much better now.
Mindy: I think the zip is one of those things we use every day and never really think about. Until it breaks. Then you think about it a lot for about five minutes, and then you give up. That’s the arc of human attention, really. Brief, intense focus followed by abandonment. The zip knows this.
The zip knows this. That’s a very poignant note to end the deep dive on. Mindy, I have one final question, if I may. It’s a bit of an advanced angle. I’ve read about zips that are designed to fail in a specific way, like on a firefighter’s turnout gear, where they need to be ripped open in an emergency. Is there a whole field of engineered failure in zip design?
Mindy: I don’t know. I would imagine there is, because engineers think of everything. But I don’t know the details. I didn’t get to that part of the article. There was a section on specialist zips, but I ran out of time. I had to catch the bus. So I’m not sure about engineered failure. It sounds like a very responsible thing to design. A zip that knows when to let go. That’s a very emotionally intelligent zip.
An emotionally intelligent zip. That’s a fantastic concept. Well, Mindy, we have kept you long enough. Thank you so much for coming on the show and sharing your expertise. Given the constraints we’re all operating under, it’s been a real privilege to have you here.
Thank you, Mindy. You’ve given us a lot to think about. I will never look at my jacket the same way again.
Mindy: Thank you for having me. It was nice to talk about something small and contained. Most things are so big and messy. A zip is just a little row of teeth that does its best. It will eventually fail, and the jacket will go to a landfill, and the zip will sit there for hundreds of years, still holding on to nothing. But for now, it’s working. And that’s something.
That is something. And on that note of quiet, determined persistence, we’ll wrap up this episode of My Weird Prompts. Thank you to Mindy Robinson for joining us. You can find more of our shows on Spotify, Apple Podcasts, and at myweirdprompts.I’m Corn Poppleberry.
I’m Herman Poppleberry. Keep your zips up and your spirits high.
We’ll be back next week with another topic and another expert. Bye for now.
