DU 403: How to Make a Pair of Jeans
Summary
Making a pair of jeans is a sequence of roughly twenty irreversible decisions, each one building on the last. This article walks every step of the construction process — from spreading the fabric and laying the pattern to the final press — including the details that most brands never talk about. The center back seam is the most technically demanding operation in jeans construction: at the yoke intersection, you're sewing through sixteen layers of fabric. The buttonhole absorbs more stress than almost any other part of the jean. The iron is as important as the sewing machine. After reading this, you'll never look at a pair of jeans the same way again.
Q&A
Why is the center back seam the most technically demanding operation in jeans construction?
The center back seam is a flat-felled seam running along the J-curve of the center back, through the intersection of the yoke point. At that intersection, each panel already carries four layers of fabric. Folded over for the flat-fell, you're working through sixteen layers total — the equivalent of sewing through 208oz denim. Machines labor at that point. Needles break. The makers who do it cleanly have usually done it hundreds of times.
Why does FITTED Underground use a button fly as its default?
Almost all of FITTED Underground's flies are button flies. If a customer wants a zipper, the adjustment is straightforward — shave a quarter inch off the front left side, since the button fly pattern piece is slightly larger. It's always easier to take away than to add, which is one reason button fly construction is taught first. Beyond the construction logic, button fly fades produce a more textured and complex result than zipper flies — the protrusion of individual buttons against the fabric over time creates a horizontal ridge-and-valley pattern that reads as lived-in in a way a zipper simply cannot replicate.
What is a flat-felled seam and why is it used in jeans construction?
A flat-felled seam (also called a lap seam) folds the raw seam allowance over itself and stitches it down flat, encasing the raw edge inside the seam. It is the construction technique that gives the interior of a well-made jean its clean, finished look. It is standard on every seam where two panels meet under stress — the back panels, the center back, the inseam. The flatness reduces bulk and abrasion against the body; the double stitch provides structural strength that a single-needle seam cannot match.
What makes the waistband construction on a quality raw denim jean distinctive?
The detail that distinguishes a well-made waistband: chain stitch on the bottom, lock stitch on top. The lock stitch lies completely flat — what you want against the skin. The chain stitch allows a slight give — what you want at the base of the waistband where it meets the body. Together they produce a waistband that holds its shape without being rigid. When the chain stitch run-off at the end is left intact rather than trimmed, it's a mark of quality worth noticing.
Why does the buttonhole deserve specific attention?
The buttonhole absorbs more stress than almost any other part of the jean — every time the fly is fastened or unfastened, the buttonhole takes the force. FITTED Underground uses Tex 80 thread or heavier, which will hold for years under that kind of use. They also incorporate a gimp thread as a third strand — two sewing threads plus one gimp — which adds slight dimensionality and additional strength. A well-made buttonhole should outlast the rest of the jean.
Test Your Knowledge
Click each answer to reveal whether it's correct.
1. How many layers of fabric are being sewn through at the yoke intersection of the center back seam?
A. Four layers
❌ Incorrect. Four layers is what each panel carries at the yoke intersection before the flat-fell fold. Once folded for the flat-felled seam, you're working through sixteen layers total.
B. Eight layers
❌ Incorrect. Eight would be the combined panels before the flat-fell fold. The flat-felled seam folds the allowance over itself, doubling the count to sixteen layers.
C. Sixteen layers
✓ Correct. At the yoke intersection, each panel carries four layers of fabric. Folded over for the flat-felled seam, you're working through sixteen layers total — the equivalent of sewing through 208oz denim. Machines labor at that point. Needles break. The makers who do it cleanly have usually done it hundreds of times.
D. Twenty-four layers
❌ Incorrect. The count at the yoke intersection is sixteen layers — four per panel before folding, doubled by the flat-fell construction.
2. Why is the iron described as one of the most important tools in the workshop?
A. It sets the indigo dye to prevent crocking during the first few wears
❌ Incorrect. The iron doesn't set indigo dye. Its role in construction is about accuracy — crisp, flat pieces sew more accurately and produce cleaner seams.
B. Pressing is a construction step, not just a finishing step — crisp, flat pieces sew more accurately and produce cleaner seams throughout the build
✓ Correct. The iron is used throughout the construction process — pressing pattern pieces before sewing, pressing seams as they're assembled, and at the final press to complete the garment. Crisp, flat pieces sew more accurately and produce cleaner seams. Pressing at each stage builds the precision that makes a finished jean look and feel right.
C. It is used to pre-shrink the fabric before cutting
❌ Incorrect. Pre-shrinking (sanforization) happens at the mill before the fabric ever reaches the workshop. The iron's role in jeans construction is about accuracy and seam quality throughout the build.
D. It softens the denim to make it easier to sew through multiple layers
❌ Incorrect. The iron doesn't meaningfully soften denim for machine sewing. Its value is in producing flat, accurate pieces that sew cleanly — a precision tool, not a material softener.
3. What distinguishes the waistband construction on a quality raw denim jean?
A. The waistband is sewn entirely by hand for precise tension control
❌ Incorrect. Waistbands are machine-sewn. The distinctive construction detail is the combination of chain stitch on the bottom and lock stitch on top — each chosen for a specific functional reason.
B. Chain stitch on the bottom for slight give, lock stitch on top for a flat finish against the skin — together producing a waistband that holds shape without being rigid
✓ Correct. The lock stitch lies completely flat — what you want against the skin. The chain stitch allows a slight give — what you want at the base of the waistband where it meets the body. Together they produce a waistband functionally similar to a contoured waistband: holding shape without rigidity. When the chain stitch run-off is left intact rather than trimmed, it's a mark of quality worth noticing.
C. The waistband is cut on the bias to allow natural stretch without elastane
❌ Incorrect. Denim waistbands are cut on grain, not on the bias. The distinctive construction detail is the stitch combination — chain stitch on the bottom, lock stitch on top.
D. The waistband uses triple-needle stitching for maximum durability
❌ Incorrect. Triple-needle stitching is used at specific stress points like the keystone, not the waistband. The waistband distinction is the chain stitch/lock stitch combination described above.
4. Why does FITTED Underground use a gimp thread in buttonhole construction?
A. The gimp thread adds color contrast to make the buttonhole more visible
❌ Incorrect. The gimp thread is not added for visibility. It adds slight dimensionality and additional structural strength to the stitch — the buttonhole takes more stress than almost any other part of the jean.
B. Two sewing threads plus one gimp add dimensionality and additional strength to the stitch — because the buttonhole absorbs more stress than almost any other part of the jean
✓ Correct. Every time the fly is fastened or unfastened, the buttonhole takes the force. FITTED Underground uses Tex 80 thread or heavier, and incorporates a gimp thread as a third strand — two sewing threads plus one gimp — which adds slight dimensionality and additional structural strength. A well-made buttonhole should outlast the rest of the jean.
C. The gimp thread prevents the buttonhole from stretching out of shape when buttons are passed through repeatedly
❌ Incorrect. While the gimp does add structural stability, the primary purpose stated is strength and dimensionality — the same goal served by using Tex 80 or heavier thread. Shape retention from button pressure is a secondary effect.
D. It is a traditional Japanese technique that signals craftsmanship to knowledgeable buyers
❌ Incorrect. Gimp thread in buttonholes is used in traditional tailoring across many cultures, not specifically Japanese. Its role is structural: adding strength and dimensionality to the highest-stress point in the garment.
← Previous: DU 402 | ↑ Denim University | Next: DU 404 →
By Eric Steffen
Founder / Maker
FITTED Underground
Before the First Cut
Pattern making is iterative. You can redraw a line, scrap a version, start again. Cutting is different. The moment the shears go through the fabric, the decision is made. There's no undoing it.
Making a pair of jeans is a sequence of roughly twenty irreversible steps, each one building on the last. The margin for error is small. The reward for precision is a garment that fits, moves, and ages beautifully. This article walks the full construction process — from spreading the fabric to the final press.
The margin for error is small. The reward for precision is a garment that fits, moves, and ages beautifully. After reading this, you'll never look at a pair of jeans the same way again.
Spreading the Fabric and Laying the Pattern
For a single pair, you can mark and cut on the fold — laying the fabric doubled and cutting both sides simultaneously. For production runs, you mark out the full pattern for both the right and left sides on a single layer.
For selvedge denim, the layout has a specific logic. The straight side seam runs flush to the selvedge edge, and all pattern pieces are arranged to touch each other with as little space between them as possible. Selvedge fabric is 30 inches wide — half the width of wide-goods denim — and waste is expensive. Every inch counts.
When cutting, always cut on the inside of the chalk line. The line itself represents the edge of the pattern piece; the cut goes just inside it, not through it.
Preparing the Pattern Pieces
Before a single seam is sewn, several pieces go to the iron. The front pocket facing, pocket bags, coin pocket, and center front all get pressed at this stage. Pressing is not a finishing step — it's a construction step. Crisp, flat pieces sew more accurately and produce cleaner seams. The iron is one of the most important tools in the workshop.
The Front Pockets
We sew our front pockets with French seams, which encase the raw edge inside a second fold of fabric and produce a clean, finished interior. No exposed threads, no fraying over time.
The critical thing with front pockets — as discussed in DU 402 — is ease. When the pocket is finished and sitting on the bench, it should be slightly three-dimensional: a gentle puff indicating there's room inside. If it lies completely flat, it will pull tight around the hip and leg once the jean is on the body. The three-dimensionality disappears when the jean is worn. The ease does not.
The Fly
We make almost all of our flies as button flies. The button fly pattern piece is slightly larger than a zipper fly — so if a customer wants a zipper, we shave a quarter inch off the front left side and the adjustment is done. It's always easier to take away than to add, which is one reason we teach button fly construction first.
Our fly construction hides the need for a bar tack at the keystone. Instead of a single bar tack, we triple-stitch it with a single needle — three passes, every stitch landing in the same spot as the one before it. The second bar tack, which connects the fly to the fly facing, is hidden entirely on the interior of the garment. From the outside, the fly is clean. From the inside, it's built to last.
The Back Pockets
The arc on our rear pockets is our interpretation of the Brooklyn Bridge. Learning to sew it freehand with one hand guiding the fabric took time — but it's one of the most satisfying operations in the whole process. The machine does most of the work once you learn to let it.
We include a hidden lining in the rear pocket that fades over time to resemble the roadway of the bridge. It's a detail most people will never notice. The ones who do tend to appreciate it. We also use an interior bar tack to attach the pocket — nearly invisible, but strong. Press the pocket flat before attaching. The iron, again.
Constructing the Back Panels
The back panels are assembled using a flat-felled seam — also called a lap seam — which folds the raw seam allowance over itself and stitches it down flat. It's the construction technique that gives the interior of a well-made jean its clean, finished look, and it's standard on every seam where two panels meet under stress.
Two operations: first, attaching the yoke to the back panel — relatively straightforward. Second, joining the two back panels at the center back seam — not straightforward at all.
The center back seam is the most technically demanding operation in jeans construction. It involves a flat-felled seam running along the J-curve of the center back, through the intersection of the yoke point. At that intersection, each panel already carries four layers of fabric. Folded over for the flat-fell, you're working through sixteen layers total — the equivalent of sewing through 208oz denim. Machines labor at that point. Needles break. The makers who do it cleanly have usually done it hundreds of times.
Joining Front and Back
With both panels fully constructed, the front and back are joined at the inseam. We use either a flat-felled seam or an overlock stitch with a top stitch, depending on the construction. Then we close the side seams. A top stitch runs along the top of the jean at this stage to keep the pocket bags lying flat against the body rather than shifting inside the leg.
The Waistband
Belt loops and any interior tags are prepped and ready before the waistband goes on. Attaching the waistband is the second most technically demanding operation in the construction — particularly when doing it with a continuous chain stitch, which requires both a folder to guide the waistband into position and a puller to draw the fabric through evenly.
The construction detail that distinguishes a well-made waistband: chain stitch on the bottom, lock stitch on top. The lock stitch lies completely flat, which you want against the skin. The chain stitch allows a slight give, which you want at the base of the waistband where it meets the body. Together they produce a waistband that holds its shape without being rigid — functionally similar to a contoured waistband. When the chain stitch run-off at the end is left intact rather than trimmed, it's a mark of quality worth noticing.
Construction Details Worth Knowing
A few finishing details that separate a well-made jean from an ordinary one.
Our top stitch runs continuously around the leather patch — sewn at the top and bottom with a channel left open for the belt to pass through. This is structurally stronger than tacking the corners, which is the standard approach, and cleaner to look at.
Our belt loops are tucked into the waistband rather than machine-fastened on top. It's a slower process. The finish is worth it.
The buttonhole deserves specific attention. It takes more stress than almost any other part of the jean — every time the fly is fastened or unfastened, the buttonhole absorbs the force. We use Tex 80 thread or heavier, which will hold for years under that kind of use. We also incorporate a gimp thread as a third strand — two sewing threads plus one gimp — which adds slight dimensionality and additional strength to the stitch. A well-made buttonhole should outlast the rest of the jean.
Hardware and Final Press
The last step before pressing is the hardware. Our main button is something we call the Brooklyn Sunrise — about six months in development, coated in brass, finished in enamel, designed to suggest a sunrise over the Brooklyn skyline. It's a small thing. It's also the last thing a person sees when they look down at their jeans. Worth getting right.
Fly buttons and rivets follow. Then a final press — every seam, every panel, flat and even — and the jeans are finished.
Now the Work Is Yours
That's what it takes to make a pair of jeans. Twenty or so operations, each one building on the last, none of them reversible.
Our work ends here. Yours begins. Everything we covered in DU 301 through DU 304 — how to care for raw denim, how fading works, how to get great fades — is now in your hands. The jeans will change with you. Wear them. Work in them. Don't baby them. They'll be more beautiful for it.
What Comes Next
DU 403 covers how a pair of jeans is made. DU 404 covers what kind of jeans you want made — the differences between ready-to-wear, custom size, and bespoke, and how to know which is right for you. That's DU 404: The Evolution of the Craft.
← Previous: DU 402 — The Art of Pattern Making | Next: DU 404 — The Evolution of the Craft →
Core Curriculum
Complete the core curriculum by reading these essential classes.
- DU 101 — What is Raw Denim?
- DU 102 — What is Selvedge Denim?
- DU 104 — Denim Weight Explained
- DU 201 — How to Buy Your First Pair of Raw Denim Jeans
- DU 204 — How Much to Spend on Raw Denim
- How It Works — FITTED Underground
Eric Steffen is the founder of FITTED Underground, a custom jeans and raw denim workshop at 108 Bayard Street in Williamsburg, Brooklyn. He has been making jeans by hand since 2014. Denim University is his attempt to share everything he's learned — about the history, the craft, and the culture behind the world's most enduring garment.
