Slubby Denim vs. Neppy Denim and Why it Matters

When you get into higher-end denim products, you’ll quickly encounter words like raw, selvedge, sanforization — all interesting terms that are worth diving into (hey look, I just linked them), but they don’t have a ton to do with the denim’s feeling and texture.

At least, not as much as the two words we’re getting into today: slub and nep. In short, both are flaws in fibers that were more common when weaving denim was more low-tech.

But the modern story of slub and nep isn’t as simple as it’s often made out to be, so we spoke with Alejandro Jomar, a tailor who runs a popular raw selvedge denim YouTube channel and Mohsin Sajid, denim expert and lecturer, and Lennaert Nijgh, founder of Benzak Denim Developers to better understand how brands create unique fabrics with slub and nep.

What is Slubby Denim?

• Uneven yarns that create a unique texture and look in denim fabrics
• Slubby yarn is made when the cotton is spun

Slub is a soft, thick, uneven section of yarn or thread. The unevenness provides texture that some people find desirable and others see as an imperfection. “A slub yarn is typically made using older spinning machinery, which causes the yarn to vary in thickness, going from thin to thick along its length,” says Lennaert. “This creates a streaky, irregular texture that’s visibly uneven, rather than smooth or uniform.”

Slubby yarn creates a woven fabric with raised streaks or stripes on its surface. If the fabric deliberately leans toward slubbiness, the jeans can look a little wavy from a distance.

Denim is just one famous example of slubby cotton, examples range from slubby t-shirts to hoodies. The yarns’ varying thicknesses create more texture than you typically find in modern fabrics.

All denim fabric has warp (vertical) and weft (horizontal) yarn threads. Usually, warp threads are dyed with indigo and make up most of the visible surface of denim. So typically, slub means the indigo-dyed warp yarns of denim vary in thickness.

Why People Like Slubby Denim

• Creates a rough and rugged texture
• Mimics the look and feel of historical denim

If you’re into this sort of denim, you’ll understand that the unique aesthetics are often a big part of the appeal. (Plenty of popular brands, like Iron Heart, are known for the opposite: making very smooth denim on shuttle looms, which is a feat in its own right. But I digress.)

“Personally, I love texture,” explains Lennaert. “It’s the same reason people love linen — it’s full of texture, and that irregularity is part of its beauty.”

It’s fun to have a garment with a bit of character that reproduces what might otherwise be a bygone era of more analog manufacturing techniques. Despite technically being imperfect, denim heads counterintuitively like these flaws in their fabric because they make each garment unique.

“You can find slub in Tescos and Sears and Uniqlo. It’s not about price.” Mohsin explains, “You can also get slub on modern looms. It’s not unique to shuttle looms. It’s more likely to be found in selvedge denim because of their customer base, but slub is about the spinning process rather than the loom that weaves the denim.”

As it ages, slubby jeans also wear out a little more unevenly, creating fades that are more dramatic and unusual than you might see otherwise.

How Textile Mills Make Slubby Denim

• Most brands design their own slub pattern on a computer

Almost all mills on earth produce denim on projectile looms. But a hundred years ago, they were usually made on shuttle looms. These looms make denim ten times more slowly and are expensive to maintain.

“Traditionally, slub was a defect. However, modern consumerism, driven by the desire to feel unique, has embraced it as a feature,” says Alejandro. “To meet this demand, many textile mills specially calibrate looms to replicate slubby textures, often to an even higher degree than produced by antique shuttle looms. This makes the texture more appealing and adds character to the garment.”

Most of the time, when someone points out a jeans’ slub, it’ll be pretty faint streaking you need to squint to look at. But again, some brands lean in to purposely amp up the slubbage.

“The kind of loom you’re making denim on does help, but you get slubby textures from the spinning process of cotton.” Mohsin says, “It’s also not always a product of vintage looms — some brands have computer programs linked to the spinning machine to produce and control a slub pattern. That’s why today, you can one-to-one recreate fabrics from the 19th century.”

How Does Slubby Denim Fade?

• Slubby jeans tend to have more vertical and stripey fades than other types of denim

When you think about fading in jeans, the fabric’s texture matters a lot: the thick parts of the yarn absorb more indigo than the thin parts, causing the dye to fade at different rates. Also, the more a thread ‘sticks out’ from a surface, the more it will face friction and rub the indigo dye, revealing the white cotton underneath. 

Slubby jeans tend to have a more vertical, stripey fade than other types of denim. This characteristic is so special that it even has its own name in Japanese: Tate-Ochi, or “vertical falls.”

What is Nep?

• Nep is when small knots of fiber are embedded in yarn
• “Neppy” fabrics have visible knots on the surface

Now, you’re a newly minted slub snob, but you might still wonder: what are the differences between slub and nep?

“It’s similar to regular yarn, but with some loose cotton fibers that poke through the warp,” explains Lennaert. “Nep refers to small knots of fiber embedded in the yarn. Fabrics described as neppy have these visible knots scattered across the surface.”

Like slub, nep is another type of imperfection in yarn that adds texture to the fabric. When jeans are made with neppy fiber, small yarn fibers protrude slightly from the surface of the denim. These give the denim texture and a sort of old TV-static constellation of fiber pinpricks.

Up close, these are little knots in the cotton, sort of tiny broken loose ends, but from a distance, they just look like snow. Or, if you’re talking to a total stranger who doesn’t understand this stuff, they’ll tell you it looks like there’s lint all over your jeans. Forget that guy!

How Does Neppy Denim Fade?

• Nep tends to lighten with wear, and the jeans look more snow-covered as they fade

As neppy jeans age, the exposed knots become even more pronounced, creating more of that beloved snowy effect. When you wear neppy denim, the little bobs of yarn are tugged on and abraded, exposing more of their white surface. While slub fades more vertically, neppy denim fades both horizontally and vertically.

“Textured fabrics tend to create more friction,” says Lennaert. “So when you rub two textured materials together, especially something like slub, which is more abrasive, it wears away the indigo dye, which sits on the surface like paint.”

Texturally, neppy jeans also tend to get fuzzier as the fibers become more exposed, so rest assured that with time, your pants will have a distinct story to tell.

“As your jeans fade, the white core of the yarn starts to show through,” explains Lennaert. “That’s why slubby or neppy fabrics tend to have more dynamic fades, with sharper contrasts between highs, lows, and worn areas.”

Wrapping Up: The Greater Significance of Slub and Nep

On a broader scale, we might ask ourselves why nep and slub are so important to denim enthusiasts. While the answer is certainly wrapped up in a deep love of vintage manufacturing techniques and their emphasis on quality and individuality, I think we can also nod to a more human undercurrent.

We’ve discussed how the aging of slub and nep is tied with a personal narrative of each garment and how, while they’re unique from the get go, these “flaws” create even more distinctive looks.

As always, the fades are a direct result of your pattern of use, reflected visually. This pattern is more pronounced when you have more slub and/or nep.