How Denim Is Made: The Complete Manufacturing Process from Cotton to Selvedge Jeans (2026)

Denim is made through a six-stage manufacturing process: cotton is spun into yarn, the warp threads are rope-dyed with indigo, the warp and undyed weft are then woven on a loom (vintage shuttle looms for selvedge, projectile looms for mass production), the finished fabric is sanforized (or left unsanforized), inspected, and finally cut and sewn into jeans. The difference between a $40 pair from a fast-fashion brand and a $400 pair of Japanese selvedge denim comes down to which version of each of those six steps a mill chooses — and Japanese mills in Kojima, Okayama, and Osaka still use 1950s-era American shuttle looms to weave the slowest, densest, most characterful denim on Earth.

At Japan-Denim.com, we work directly with the Okayama and Osaka mills that supply Iron Heart, Momotaro, Studio D'Artisan, and Oni. This is the full process — explained for US and Canadian buyers who want to understand what they're actually paying for when they buy a pair of raw selvedge jeans.

What Is Denim?

Denim is a sturdy cotton twill fabric in which the warp threads are dyed (almost always with indigo) and the weft threads are left undyed (natural white or ecru). That single design choice — dyed warp, undyed weft — is what gives denim its signature look: blue on the outside, white on the inside, and the gradual high-low fading that develops as the indigo wears off the surface of the warp yarn over months of wear.

The name comes from serge de Nîmes ("fabric from Nîmes"), a sturdy French twill that 19th-century American mills like Amoskeag and Cone Mills adapted into the workwear fabric we now call denim. By the 1960s, Japan had begun importing American denim, and in 1965 Kojima-based Big John produced the first jeans made entirely on Japanese soil. Sixty years later, the Kojima-Okayama corridor is the global center of premium selvedge production.

The 6 Stages of Denim Manufacturing

Stage 1: Cotton Selection and Spinning

Every pair of jeans starts as raw cotton fiber. Japanese mills prize long-staple cottons — Zimbabwean, American Pima, Texan, and Egyptian — because longer fibers spin into stronger, more uneven yarns that fade with more character. Ring spinning (an older, slower method that produces irregular, slubby yarn) is preferred by Japanese mills like Kuroki, Kaihara, Collect, and Nihon Menpu over the faster open-end spinning used by mass-market producers. That slub — those tiny variations in yarn thickness — is what creates the textured, three-dimensional fades that Japanese denim is famous for.

Stage 2: Rope Dyeing the Warp with Indigo

Only the warp threads are dyed. The yarn is twisted into thick "ropes" and dipped repeatedly into vats of indigo dye — typically 6 to 16 dips, depending on how deep the mill wants the indigo to penetrate. Critically, indigo is a ring-dyeing agent: it bonds to the outside of each yarn but never fully penetrates the core. That's why raw denim fades to white inside the yarn as you wear it — the colored shell rubs off and exposes the undyed core. Japanese mills like Kuroki and Collect are famous for using natural indigo (aizome) sourced from Tokushima Prefecture, which produces a deeper, more complex blue than synthetic indigo.

Stage 3: Sizing and Warping

After dyeing, the indigo warp yarns are coated in starch ("sized") to strengthen them for weaving, then arranged in parallel on a beam — typically 3,000 to 5,000 warp threads sitting side by side. The undyed weft yarn is wound onto separate bobbins. The denim is now ready to be woven.

Stage 4: Weaving — Shuttle Loom vs Projectile Loom

This is the single biggest variable in denim quality. Vintage shuttle looms — almost all of them American Draper X3 looms from the 1940s–1960s — weave slowly (about 150 picks per minute) on a narrow loom about 30 inches wide. Because the weft yarn is carried back and forth by a single shuttle, the edge of the fabric is self-finished with a tightly woven "selvedge" (self-edge) band. This is what creates the white-and-red selvedge ID line you see on the cuff of high-end jeans. Modern projectile or air-jet looms weave four times faster (600+ picks per minute) on wide bolts (60+ inches), but the weft is cut at the end of every pass, leaving a frayed edge that has to be overlocked. That's "non-selvedge" or "open-end" denim. The shuttle-loom denim is denser, more irregular, and ages with far more character — but it costs roughly 5–10x more to produce.

Stage 5: Finishing — Sanforized vs Unsanforized (Loomstate)

Right off the loom, denim shrinks 8–10% on first wash. To stop this, most mills sanforize the fabric — running it through a steam-and-roller process that pre-shrinks it. The result: jeans that fit the same after wash as before. Japanese mills also offer unsanforized ("loomstate") denim, which skips that step. Unsanforized jeans must be soaked or worn-in-the-tub by the buyer to shrink them to their final size, but the fabric retains a hairier, more textured surface that fades with extra dimension. Brands like Iron Heart, Samurai, and Oni all offer unsanforized lines.

Stage 6: Cut, Sew, and Quality Control

The finished denim is cut according to the pattern, then sewn — usually with chainstitch hems (using vintage Union Special 43200G machines), copper rivets at stress points, and heavy-duty cotton thread that contracts when washed, creating the famous "roping" effect at the hem.

Best Options: Where the World's Best Denim Is Actually Made

Not all denim is created equal. Here are the mills and brands that represent the highest end of each stage of the process.

Kaihara Mills (Hiroshima, Japan)

• Best for: The world's most consistent premium denim — supplies UNIQLO, Levi's Made in Japan, and APC
• Key specs: Founded 1893 (originally a kasuri kimono dyer); rope dyeing with up to 24 indigo dips; both shuttle and modern projectile looms
• Price range: Jeans made with Kaihara denim typically run $80–$250 USD
• Why we recommend it: Kaihara is the entry point into authentic Japanese denim — the consistency and quality at the price are unmatched globally.

Kuroki Mills (Ibara, Okayama)

• Best for: Heavyweight, character-rich shuttle-loom selvedge in the 14–18 oz range
• Key specs: Natural indigo dyeing; vintage American Draper looms; slubby ring-spun yarn
• Price range: Jeans made with Kuroki denim typically run $250–$500 USD
• Why we recommend it: Kuroki supplies the denim for many of the cult Osaka Five brands. The fades are unbeatable.

Collect Mills (Inc.) — Kojima, Okayama

• Best for: Ultra-heavy, ultra-textured denim (18oz–25oz) made for brands like Momotaro, Japan Blue, and Iron Heart
• Key specs: Natural indigo plus synthetic blends; specialty looms tuned for slub; cult "Memphis" and "GTB" denims
• Price range: Jeans made with Collect denim typically run $300–$600 USD
• Why we recommend it: If you want denim that looks like rope, feels like canvas, and fades like cracked porcelain, this is the mill.

Cone Mills White Oak (North Carolina, USA — closed 2017)

• Best for: Historical reference. American shuttle-loom denim used by Levi's Vintage Clothing until production ended.
• Key specs: Draper X3 looms (the same model now running in Kojima); short-staple American cotton
• Price range: Deadstock fabric jeans now $400–$1,000+ USD
• Why we recommend it: Knowing White Oak existed (and closed) is essential context for why Japanese mills are now the last stronghold of vintage-loom denim.

Shuttle Loom vs Projectile Loom: How They Compare

Frequently Asked Questions

Q: What is denim actually made of?
A: Denim is made of 100% cotton in its purest form — long-staple cotton fiber spun into yarn, then woven on a loom. Stretch denim adds 1–3% elastane (Lycra/Spandex), and some heritage denim blends in small amounts of linen or hemp, but classic Japanese selvedge denim is pure cotton.

Q: Why is Japanese denim considered the best in the world?
A: Japanese mills like Kaihara, Kuroki, and Collect kept running vintage American shuttle looms long after US mills replaced them with faster projectile machines. The slower, narrower weave produces denser fabric with irregular slubby yarn and self-finished selvedge edges — qualities that fade into uniquely characterful patinas that mass-produced denim simply cannot replicate.

Q: What does "rope-dyed" indigo actually mean?
A: Rope dyeing twists the warp yarn into a thick rope before dipping it repeatedly into indigo vats. Because indigo bonds only to the outside of each yarn (ring dyeing), the multiple short dips create a deep blue surface with a white cotton core — the structural reason raw denim fades the way it does.

Q: How long does it take to make a pair of selvedge jeans?
A: From cotton bale to finished jean, premium Japanese selvedge takes 4–8 weeks. The weaving stage alone takes 5–10x longer than projectile-loom denim because shuttle looms run at ~150 picks per minute and the fabric is only ~30 inches wide.

Q: What is sanforization and should I avoid it?
A: Sanforization is a steam-and-roller pre-shrinking process that prevents jeans from shrinking after first wash. Most jeans (including most Japanese selvedge) are sanforized so they fit the same wet or dry. Unsanforized ("loomstate") denim retains more surface texture and shrinks 8–10% on first soak — it's preferred by purists who want to size the jeans to their body, but it requires more care during the first wash.

Q: Are American-made selvedge jeans still produced?
A: Yes, but in small quantities. Cone Mills White Oak in North Carolina — the last American mill running vintage Draper shuttle looms at scale — closed in December 2017. A handful of smaller mills (Vidalia Mills in Louisiana acquired some of the White Oak looms) and brands like Tellason and Roy Slaper continue to produce US-made selvedge, but Japan remains the global capital of shuttle-loom denim.

The Bottom Line

How denim is made is the single best lens for understanding why premium selvedge costs what it costs. Every stage — the long-staple cotton, the ring-spun slubby yarn, the natural indigo rope dyeing, the slow vintage shuttle loom, the unsanforized finish, and the chainstitched construction — is a deliberate choice to prioritize character and longevity over speed and uniformity. When you buy a pair of Japanese selvedge jeans, you're paying for that entire chain of choices.

At Japan-Denim.com, we ship Kojima and Osaka selvedge jeans direct to the US and Canada — made on the same Draper looms that once ran in North Carolina, by mills that have been weaving for 60+ years. If you want to see what 16oz of Kuroki indigo looks like in person before it fades on your legs for the next decade, our catalog is the best place to start.

Further Reading

• The History of Japanese Denim: From 1965 Big John to Global Selvedge Dominance
• Kojima Jeans: Inside Okayama, the Birthplace of Japanese Denim
• Selvedge vs Regular Denim: What's the Difference and Why It Matters
• Unsanforized Denim: The Complete Guide to Loomstate Selvedge for US Buyers
• Indigo Denim: The Complete Guide to Japan's Deepest Blue