On a technical drawing a zipper is a line. On a pattern it is a seam with a rigid object sewn into it, and moving that line by twenty millimetres can change the number of pattern pieces, the seam allowance, the way the garment hangs and the size range it can be graded into. Placement is therefore a pattern decision that happens to involve a zip, not a trim decision made at the end.

Placement Is a Pattern Decision

Every zip replaces or covers a seam, so the pattern has to provide a stable edge for the tape. A centre-front zip needs a seam allowance wide enough to hold the tape, usually 15-20 mm, and a facing or placket behind it. A side-seam zip needs the seam to be straight over its full length, which may mean shifting a curved side seam or adding a seam below the opening.

The opening also has to relate to the body's landmarks. A dress zip that stops at the waist will not let the wearer through the shoulders; a trouser fly that starts too low pulls across the seat when the wearer sits. The useful rule is that the opening must clear the widest fixed point between the entry and the exit, and that the ends of the zip should land on a stable area rather than on a curve that moves.

  • Centre front or centre back: the most predictable, because the seam is on grain.
  • Offset front, 20-40 mm from centre: a design line that also shifts the button or zip axis.
  • Side seam: discreet, but the seam must be straightened and the pocket has to move.
  • Diagonal or curved: expressive, and the most demanding on chain flexibility.

The Body Moves and the Zip Does Not

A zip has almost no stretch along its length. Any seam it sits in will therefore behave differently from a seam without one, and the difference shows first where the body bends: the waist, the seat, the elbow, the knee. A vertical zip that crosses the waist on a fitted jacket will stand away when the wearer sits unless the pattern adds a little ease or the zip stops above the waist and a button takes over below it.

Horizontal placements have their own logic. A horizontal zip across a pocket or a chest works because the load is carried by the seam rather than by the chain, but it interrupts the drape of the panel and can create a visible ridge on lightweight fabric. On stretch fabric, any zip needs a stabiliser behind it, or the seam will ripple as the knit recovers at a different rate from the tape.

Curves, Grain and Bias

Grain direction decides how a zip behaves over time. A zip on the straight grain stays straight. A zip on the bias follows the cloth as it drops, and after a day on a hanger the seam can grow by several millimetres, which is enough to make a carefully fitted opening look wavy. Bias-cut garments are better served by a stabilised seam, a shorter opening, or a closure that lives in a straight panel.

Curved zips need a chain that can turn. A coil is the practical choice for a radius under about 300 mm; metal and moulded chains want longer, gentler curves. Even with a coil, the tape has to be clipped or notched on the inside of the curve, and the seam allowance has to be trimmed after sewing so the curve does not bulk.

Grading Across Sizes

A placement that works at the sample size can fail at the ends of the range. A zip set close to the side seam may sit on the curve of the bust in a larger size, and a diagonal that reads as a design line on a small size can travel across the apex on a larger one. Zips are also sold in fixed lengths, so a placement that needs an odd length will either be cut down, which changes the stop position, or specified as a custom length.

The cure is to check the placement on the pattern at the smallest and largest sizes before the first sample is cut, not after the range is graded. It is cheaper to move a line on paper than to re-cut a block.

What It Costs

Placement costs appear in development rather than in the bill of materials. A moved zip can add a pattern piece, a fitting round and a marker revision, and each of those consumes calendar time that is usually tighter than the budget. If the move changes the seam allowance, the lining and the facing have to change with it, and the interlining pattern follows.

At production the cost is in handling. A zip that crosses a seam, a pocket or a dart takes more minutes and more skill than one in a clean seam, and the reject rate rises where two elements have to line up. Standardising placement across a collection, even loosely, lets the sample room and the line reuse the same construction and the same machine set-up.

Checks Before Cutting

  • Confirm the opening clears the widest body point in every size.
  • Check that the seam under the zip is straight or generously curved.
  • Verify grain direction and whether the seam needs stabilising.
  • Confirm the zip length exists, or specify a custom length with stop positions.
  • Walk the pattern at the smallest and largest size, not only the sample size.

YCC supplies chains in fixed and custom lengths with defined stop positions, which makes it easier to keep a placement decision intact when the pattern is graded.