A long down coat solves a different problem from a short jacket. It has to cover the seat and thighs, it is worn while sitting, driving and climbing stairs, and its own hem weight pulls on the front opening whenever the wearer moves. That is why a two-way zipper, with a second slider entering from the bottom, has become standard on this garment class. It is also why the placket fails in ways a short jacket never does.

The project described here is a typical one: a coat length of 100-120 cm, a 5 to 5.5 cm baffle, a detachable hood, and a buyer who wants the coat to open from the hem for sitting without unzipping the chest. The numbers below are starting points for a specification, to be confirmed with the actual shell and filler.

1. Requirement: load, access and wearer behaviour

Start from how the coat is used rather than from the component catalogue. Requirements usually include:

  • Bottom access: the wearer can open the lower 30-40 cm while seated, with one hand, without removing gloves.
  • Load: the hem and the lower placket carry the weight of a long coat plus pocket contents, so the chain and bottom stop must tolerate repeated peel and shear.
  • Locking: both sliders must stay where they are put; a bottom slider that creeps upward leaves a gap at the hem in wind.
  • Alignment: the two sliders must meet and pass each other without forcing, and the chain must not twist when the coat is closed from the bottom.
  • Repair: a jammed bottom slider should be replaceable without opening the whole placket.

Note that the load case is not just vertical. When a seated wearer leans forward, the lower placket is bent and the chain is loaded across its width. A chain that is adequate in straight pull can still open under this peel force.

2. Selection: chain size and two-slider configuration

A #5 nylon coil is the practical minimum for a long down coat; many projects move to a #8 coil for the extra width and better resistance to cross-wise opening. Metal chains are uncommon here because they feel cold and add weight, but a moulded plastic chain in a large size can work if the design language is sporty.

The two sliders are not identical. The upper slider normally carries an auto-lock body and a puller sized for gloves. The lower slider must also lock, but its body should be oriented so that the pull tab hangs downward when the coat is closed; a bottom slider with the wrong body orientation digs into the wearer's hand and wears against the fabric. Both sliders should come from the same production lot as the chain, because mixing lots is a common cause of a slider that runs stiffly in one direction.

The bottom stop deserves its own decision. On a two-way placket, the bottom stop is not a simple crimp; it must prevent the lower slider from running off while allowing the upper slider to park above it. Specify the stop type and its pull-off strength with the chain, and ask for a sample that has been cycled, not just a new one.

3. Key processes: assembly and placket construction

Assembly order matters more than on a one-way placket. Sew the chain to both fronts first, then insert the lower slider before the bottom stop is set, and only then crimp or mould the stop. Setting the stop too early makes insertion impossible without damaging teeth. Keep the two tapes perfectly aligned at the hem: a 1-2 mm offset is enough to make the lower slider bind at the first closure.

The hem is the second critical point. A long coat hem is usually curved, and a curved hem puts the tape under tension on one side. Either straighten the placket section for the last 10 cm or use a tape with enough elasticity to follow the curve without puckering. Interface the hem corner lightly so it does not fold over with wear.

Flap construction follows the same rule as a short jacket: topstitch through the flap only, keep the seam allowance at 8-10 mm, and extend the flap past the top stop. On a two-way coat, add a small bartack or rivet at the point where the lower slider parks when the coat is fully closed, because that is where the flap takes the most abrasion.

4. Testing and acceptance

Test the two-way function as a system, not as two independent sliders:

  • Cycle test: 3,000 cycles closing from the top and 3,000 closing from the bottom, with inspection every 500 cycles.
  • Pass test: with the coat closed, move the lower slider up and the upper slider down until they meet, then separate them; record any tooth skip or forced entry.
  • Lock test: static load on each slider in the locked position, with the coat hanging and with a 5 kg load in the pockets.
  • Peel test: with the lower 20 cm open, apply a sideways pull equivalent to a seated wearer leaning forward, and check for self-opening.
  • Wash and dry: five cycles, then repeat the pass and lock tests; tape shrinkage often appears only after the second wash.
  • Cold test: -15 degrees Celsius for four hours, then operate both sliders with a gloved hand.

Record the hand force for each operation. A two-way placket that needs two hands to close will be returned by users even if it passes a strength test.

5. Common risks and how to close them

The most frequent field failures are mechanical. A lower slider installed upside down wears the tape and jams within weeks. A bottom stop that is crimped too tightly cracks the tooth root, and the chain separates at the hem. Mixing chain lots produces a section that runs heavily in one direction. A hem that is too curved pulls the tape into a wave that catches the slider.

There are also design risks. A two-way zipper on a very light shell can look bulky; if the design insists on a #8 chain, widen the flap rather than thinning the tape. A long coat with a deep vent plus a two-way placket can create two competing openings at the hem, so decide which one the wearer uses first. Finally, brief the repair network: replacing a bottom slider requires the correct spare body and a stop-setting tool, and a coat returned for this repair should not be written off as a chain failure.