Not buildable in Clothix. The engine is built for knits; wovens are a later phase. This page is the construction knowledge — see the roadmap.
Flat-felled seams
How are jeans made, in one sentence? Five techniques, each answering a specific failure, and this is the first.
The inseam and outseam of jeans aren't overlocked. One allowance is folded over the other and both are stitched down flat, twice, which encloses both raw edges and produces the double row of contrast topstitching everyone recognises.
Why: a trouser leg seam takes tension in two directions and rubs against itself constantly. An overlocked seam in a 14 oz denim would abrade through. The flat-felled seam has no exposed edge and four thread paths sharing the load.
Cost: two passes on a specialised machine, and a real allowance — 15 to 20 mm rather than the 6 mm a knit seam takes. Which is why allowance is a per-seam decision.
The fly
Five pieces for something nobody looks at: the fly facing, the fly shield, the zip, the topstitched J-stitch, and the bar tack at the bottom. The bottom of the fly is where the most force concentrates on the whole garment when someone sits, which is why it gets a bar tack and why an unreinforced fly is a warranty claim.
Rivets
Rivets exist for one documented reason: pocket corners tore. A rivet is a mechanical fastener through the pocket corner and the front panel that puts the load on metal rather than thread.
The spec is four values — diameter, material, finish, and the exact position relative to the pocket corner — plus whether the back pockets are riveted at all. Many modern jeans hide or omit the back rivets, because a rivet at a back pocket corner scratches whatever the wearer sits on.
The curved waistband
A straight waistband on jeans gapes at the back, because a waist is not a cylinder. The band is cut with a curve — higher at the centre back, following the body's slope — and that curve is the difference between a waistband that sits and one that stands away.
Then belt loops: five or seven, positioned relative to the centre front and centre back, each bar-tacked at both ends. A belt loop that isn't bar-tacked comes off, and the tack is the cheapest stitch on the garment.
What a jeans tech pack adds
| Beyond a knit top | What to specify |
|---|---|
| Rise | Front rise and back rise separately. This is the measurement that decides the fit. |
| Inseam and outseam | Both. If they disagree with the rise, one of the three is wrong. |
| Thigh, knee, leg opening | Three points down the leg define the taper. |
| Seam types per seam | Flat-felled, lockstitch, chainstitch — with allowances and thread weight. |
| Topstitch thread | Colour and weight. It's the most visible decision on the garment. |
| Rivets and tacks | Position, material, finish, count. |
| Wash and finish | A separate specification from the fabric, with its own supplier. |
| Shrinkage | Raw denim can lose 5 to 10 % in length. It goes in the pattern. |
The number that catches people
Shrinkage. A raw, unsanforised denim losing 8 % of a 105 cm inseam is 8 cm — the difference between a fit and a return. It has to be added to the pattern, and whether your measurement chart is stated pre-wash or post-wash has to be written down where nobody can miss it. Selvedge, raw and unsanforised are three separate claims.
Denim weights and twill direction · selvedge · seam allowances by machine · all garment categories · when wovens arrive