The Science Behind Your Unraveling Sweaters

7:53 minutes

Unraveling a knitted product. The hand pulls the threads from the knitted fabric.
Sweaters aren’t what they used to be. Credit: Shutterstock

It’s sweater season once again, but you may have noticed that some of your newer sweaters aren’t standing the test of time. Perhaps they are pilling, unraveling, or losing their shape. But if you look at sweaters from the ‘80s or ‘90s, they may still look brand new. Last month, an article by Amanda Mull in the Atlantic about declining sweater quality made the rounds online, and we wanted to know more.

What, scientifically, went wrong in sweaters? And why are sweaters so bad now?

Guest host Flora Lichtman unravels the science of sweaters with Dr. Imran Islam, knit expert and assistant professor at the Fashion Institute of Technology in New York City. They chat about the fibers that make up sweaters, what physics has to do with how long they last, and what to look for when purchasing knitwear.

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Segment Guests

Imran Islam

Dr. Imran Islam is a textile science professor and knit expert at the Fashion Institute of Technology in New York, New York.

Segment Transcript

FLORA LICHTMAN: This is Science Friday. I’m Flora Lichtman. It is officially sweater weather. Time to pull out those chunky weaves.

Now I look forward to this annual ritual, but I have noticed that my new sweaters often look like they’re hanging on by a thread while my old sweaters still look brand new. Is this real? And why?

Why do sweaters suddenly seem to stink? Today, we are unraveling sweater science with Dr. Imran Islam, knit expert and assistant professor at the Fashion Institute of Technology in New York City. Welcome to Science Friday.

IMRAN ISLAM: Thank you.

FLORA LICHTMAN: OK, well, what is your approach to sweaters? Do you just invest in one great sweater and that’s it for you?

IMRAN ISLAM: Yes. I would say yes.

FLORA LICHTMAN: I’m relieved. OK, please keep going. In what way?

IMRAN ISLAM: Well, if you look at the statistics currently, approximately 62% of the textile fibers are synthetic fibers like polyester, nylon, acrylic, that sort of thing. So typically, when we say sweater, historically, sweater based on wool fiber and some sort of cashmere, that kind of exotic fiber, too. There was a little bit of cotton, too, at some. Point but nowadays, it’s mostly acrylic, polyester, that kind of material more and more you will find in the sweater.

FLORA LICHTMAN: But why is that worse? Why does that translate to my sweaters falling apart?

IMRAN ISLAM: Well, definitely all this natural fiber I just mentioned, wool, or cashmere, or cotton, they do have inherent property that goes with the thermal insulation. Let’s say wool has some sort of crimped or wavy shape when those are collected from the sheep. And when you make the fabric out of it, because of the wavy shape of the fiber, there is air pocket. Within the air pocket, there is trapped air that’s used as a natural insulator. So wool has an inherent thermal property.

Now for manmade fiber, you have to recreate that. That’s number one. So something inherent versus something recreated, like regenerated. So these are one difference.

FLORA LICHTMAN: Right. The imitators are always not as good as the original.



IMRAN ISLAM: And another thing is I would say the moisture properties. So wool is known as hygroscopic. So hygroscopic means it absorbs water but keep it inside the cell, but the outside seems dry. But still, it absorbs water. And cotton absorbs thoroughly. But if you think about the polyester or acrylic, they don’t absorb. They are hydrophobic fibers.

And what happens is that when there is a friction, because most of the time, we wear a sweater on top of something. It is our topmost dress or article when you wear. There must be something inside. So there is a constant friction when you wear one dress on top of another.

And because of the friction, there is a static electricity. And then also some of the fibers are broken on the surface. So broken fibers and also static electricity, these two combine together so that all the broken fibers come close to each other, they form a fiber ball, which you know as pilling.

FLORA LICHTMAN: Oh, I know pilling, believe me.

IMRAN ISLAM: So specifically when you wear, let’s say, acrylic, especially nowadays if you go to the market, if you see something very cheap, you see the peeling right after a few days. You’re going to see that. You witness that.

But in the previous one, you used the wool and cashmere or that sort of thing, it tends to generate less static electricity and tends to form less pilling.

FLORA LICHTMAN: Basically because of the structure of the fiber and because it can absorb water rather than repel it, it seems like these are the key reasons why these natural fibers do better.

IMRAN ISLAM: Exactly. Yeah. Exactly.

FLORA LICHTMAN: I want to look at my sweater right now to see what it says about its makeup. And OK, it says it’s 85% polyester, 15% nylon.

IMRAN ISLAM: So I believe for your sweater, the 15% nylon is to give it a little bit of strength because nylon is known for a stronger fiber. If you remember some of the nylon cord we used to tie something.


IMRAN ISLAM: So the purpose– basically, the sweater should be 100% polyester for that one. But the producer, they add a little bit of nylon just so that–

FLORA LICHTMAN: So I could get it over my head.

IMRAN ISLAM: Yes. Probably it will give you a little bit of strength. Will a little bit reduce the pilling property. But again, the warmth you are looking at when they produce the fibers are straight, it comes through a device called a spinneret. It looks like your shower head.

Do you remember the shower head? When you drop the water, water is coming straight from there? So the manmade fiber, they produced like that. So those are straight. But in order to get the thermal insulation property, there is a particular technological texturization. So basically, all the straight fibers becomes zig-zag shape so that it will hold–

FLORA LICHTMAN: They perm the fibers, yeah.

IMRAN ISLAM: Right, they perm the fiber. Exactly. That would be the best way to describe. And then within the cone shape, they tried to imitate that air pocket that you are getting inherently from wool, or other natural fiber. So that air pocket tends to help them to be natural insulator or something.

FLORA LICHTMAN: So I’m assuming that what we’re talking about, the move away from natural fibers isn’t just happening with sweaters. This sort of degradation in quality must be part of this bigger fast fashion story problem. Is that true?

IMRAN ISLAM: Yes, that’s true. Basically, the more you are going away– again, if you remember like 10, 15 years– or 20 years ago, we used to have one or two sweaters per winter or something like this. So now it is if you look for the people, they have a number of sweaters in their closet, even for the same winter. So that is one of the reasons.

People have a high level of demand of different types of articles within the sweater category. And to cope up with the supply and demand, producer has to go through a route. Like for instance, in order to– if you want to think about wool, you have to think about the all natural variabilities, or if you think about the cotton, you have to think about all the natural things that you cannot control much. It goes with the weather and some sort of thing, like natural ingredients.

But for synthetic materials like polyester or acrylic, you can make it in a lab and in a bulk quantity with a less with a lesser price. You have to deal with less number of variables. Most of the things are under your control.

So in order to adapt the fast fashion and supply and demand, the manufacturer rely upon more of synthetic fibers. And also, since you are buying more articles for the same season, that means you are not willing to pay more for one article.

FLORALICHTMAN: My next sweater is going to be thrifted. That is what I’m taking from this. I’m going to go back to the ’80s, I don’t know, maybe ’90s. That seems like the era I need to be looking in.

IMRAN ISLAM: Yeah. I mean, thrift store would be another good way. Definitely the wool sweater and everything, they have longer lifetime. And thrift store would be a good way to get them easily.

FLORA LICHTMAN: Thank you for joining me today.

IMRAN ISLAM: You’re welcome.

FLORA LICHTMAN: Dr. Imran Islam is a knit expert and Assistant Professor at the Fashion Institute of Technology in New York City.

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Rasha Aridi is a producer for Science Friday. She loves stories about weird critters, science adventures, and the intersection of science and history.

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Flora Lichtman was the host of the podcast Every Little Thing. She’s a former Science Friday multimedia producer.

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