Fastenings are the moving parts of a garment. Nearly everything else is fixed once it is sewn. A zip, a button, a snap, a drawcord and an elastic waistband all move every time the garment is worn, washed and dried.
The useful thing about fastening failures is that they are not random. Each type fails in a small number of predictable ways. Each of those ways can usually be prevented by something you write in the specification before production starts. This piece goes through the five common functional fastenings, what actually breaks in each, and what to write down.
Zips: the slider usually fails before the teeth
A zip has four parts that matter: の tape (the woven strip it is built on), の chain (the teeth or coil), の slider, そして stops at each end. Buyers tend to write “zip” in the tech pack and leave the rest to the factory. Each of those four parts has its own failure.
The three chain types behave differently under strain
- Nylon coil. A continuous nylon monofilament coiled and stitched to the tape. Light and flexible, so it follows a curved seam without fighting it. It is also the most forgiving: if the chain is forced apart under sideways strain, the coil usually springs back and re-meshes when you run the slider over it again.
- Moulded tooth. Individual plastic teeth moulded onto the tape. Stronger than coil in a straight line and much better in dirt and grit. But it is stiff, so it does not sit well on a curve, and a stressed tooth does not bend back. It cracks or snaps off, and the zip is then finished.
- Metal. Individual teeth clamped onto the tape. Strong, and the look most buyers want on denim and outerwear. The failure is the clamping: a tooth that is pulled sideways hard enough works loose from the tape and comes off. One missing tooth means the slider passes the gap and the zip opens behind it.
The practical consequence is a design decision, not a cost decision. A curved seam, a light dress, a soft resort garment — coil. A load-bearing front opening on a heavy garment — moulded tooth or metal. Putting a stiff moulded chain on a curved opening will produce a zip that ripples and a customer who thinks the garment is badly made.
Why sliders stop holding
The slider is doing the work. Its two plates squeeze the two sides of the chain together as it passes, and hold them meshed behind it. Over thousands of cycles the slider body wears and slowly spreads. Once the gap between its plates is a little too wide, it stops pressing the chain fully closed, and the zip splits open behind the slider while the slider itself still moves normally.
This is the single most common zip complaint, and it is almost always read by the customer as “the zip broke”. Nothing broke. The slider stopped gripping. It is also why the cheapest available slider on an otherwise decent chain is a false saving — the part that wears out first is the part that was downgraded.
Two other slider problems are worth knowing. の pull hangs from a small loop called the bail, which flexes through the same bend every time the zip is used and can eventually fatigue and break — the chain is fine, but there is nothing left to hold. And on plated metal sliders, the plating chips with wear, which exposes bare metal that then corrodes and stains the garment around it.
An auto-lock slider has a small pawl that drops into the chain whenever the pull is released, so the zip cannot creep open under load. On any closure that carries weight or sits under tension while worn, specify it. A non-locking slider on a fitted skirt or a jacket front will slide down on its own and the garment will be blamed.
Separating zips fail at the bottom
A separating (オープンエンド) zip has a pin on one side and a retainer box on the other. The pin drops into the box and the box holds both sides square while the slider starts. If the box cracks, or the pin bends, the two sides no longer align and the zip either will not start or splits from the bottom upward. This is not repairable in the field — the whole zip has to come out. On any garment with an open-end front, the box and pin should be a specified quality point, not an afterthought.
A wavy zip is a setting problem, not a zip problem
A zip that ripples along its length is usually the fabric and the tape disagreeing. Zip tape is stable and hardly stretches. A soft viscose, a light rayon or a bias-cut opening stretches easily under the presser foot. The fabric is fed in slightly longer than the tape, and when the pressure comes off, the seam waves.
The same thing happens after the first wash, for a different reason: a cotton or linen shell shrinks and a polyester tape does not, so the tape now has more length than the fabric it is sewn to. The fix in both cases is at the cutting table — stabilise the zip opening with a strip of light fusible or stay tape before setting the zip, and make sure fabric and trim are tested for shrinkage together, not separately. How the seam itself is stitched is a separate subject, covered elsewhere on this site.
特定: chain type (coil, moulded, metal); chain size, written as the industry number — ある #3 chain is about 3 mm across, ある #5 about 5 mm, ある #8 heavier again; closed-end or separating; auto-lock or free slider; tape colour and whether it is dyed to match or contrast; slider and pull finish; そして, for metal, whether the finish is plated or solid. Ask for a sealed zip sample and keep it.
Buttons: the button rarely breaks, the attachment does
Buttons themselves are usually fine. What fails is how they are held on, and how they pass through the hole.
あ shank is the stem that lifts the button off the fabric surface. It exists to leave room for the layer of cloth that comes up through the buttonhole and sits under the button when the garment is fastened. Without that clearance the button is pulled hard against the fabric every time it is done up, and all of that force goes into the threads holding it. On a shirting weight fabric a flat sew-through button is fine. On anything thick — a coat, a heavy jacket, a quilted or padded panel — either use a shank button, or specify that the flat button is attached over a thread shank, which is a deliberate slack loop of thread that does the same job.
Attachment failure has three common shapes. Too few thread passes, so the small number of threads carry all the load and abrade through. No securing at the end of the attachment, so once one thread wears the whole thing unravels and the button drops off intact. And a button attached through a single layer of light fabric with nothing behind it, which does not tear the thread at all — it tears the fabric, taking a hole with it. On any button under real load, specify a reinforcement behind it: an interlining patch, a backing button on a coat, or attachment through a facing rather than a single layer.
Buttonholes cause as many complaints as buttons. Too tight and the customer forces the button through, which stretches the hole and eventually splits the end of it. Too loose and the garment gapes and the button works itself undone. The working rule is that the buttonhole length equals the button’s diameter plus the button’s thickness; for a thin flat button that comes out at roughly the diameter plus about 3 mm. A domed, covered or toggle button needs more. Buttonholes must also be cut cleanly and their ends secured — a frayed end grows on every wash.
特定: button size in ligne or millimetres, 材料, shank or sew-through, thread colour, number of thread passes, what reinforcement sits behind the button, buttonhole length and orientation, そして — for tack or jeans buttons — that the attaching machine setting has been proved on the actual fabric thickness. If the button is metal and will touch skin, ask the trim supplier for their nickel-release test result; several markets regulate this.
Snaps and press studs: four parts, and only one of them is a spring
A press stud is four pieces working as two pairs. の cap そして socket make one half; の post (or eyelet) そして stud make the other. Each pair is squeezed together through the fabric by a press, so the fabric is clamped between them. The closure itself is the socket gripping the stud, usually by a small spring ring inside the socket.
That gives two completely separate failures, and they need different fixes.
- The closure fails. The snap pops open on its own, or opens under light load. The spring in the socket has been opened and closed enough times to lose its tension, or was too weak for the job in the first place. For anything under real strain, ask the trim supplier for a stronger action socket rather than the standard one. A row of weak snaps down a front placket will open when the wearer sits down.
- The attachment fails. The whole snap tears out of the fabric, taking a hole with it. This is a pressing and a fabric problem, not a snap problem. Too little press pressure and the two halves never lock together. Too much and the post is crushed and cuts the fabric fibres around it. And a snap set through a single layer of light cloth has almost nothing to hold on to.
Snaps always need a firm ground. Set them through a facing, a placket or an interlined panel — never through one layer of a light fabric alone. The press setting has to be proved on the real construction, at the real thickness, before the line starts, and re-checked when the fabric or the interlining changes.
特定: snap size and type (ring spring, prong, or a heavier post type), the strength of socket action, the finish, the exact layers it is set through, and that a pull-off and an opening check are done on the sealed sample.
Drawcords: the two failures are both about the ends
A drawcord is a cord running through a channel, with an opening at each end. Its problems are almost all at the ends and at the channel, not in the middle.
The cord disappears into the channel. The customer pulls one side, the other end vanishes inside, and it cannot be threaded back without a tool. The standard prevention is a bar tack through the cord and the channel at the centre back or centre front, which fixes the midpoint of the cord in place and lets both ends move freely. A knot or a moulded stopper larger than the eyelet does the same job at each end. One of the two should always be specified.
The cord end frays. A cut cord end unravels and then will not pass through the eyelet. The end is finished either with a heat seal, a crimped metal or moulded tip, or a dipped and cured coating. All of them work; what matters is that the finished tip is narrow enough to pass the eyelet easily and firm enough not to soften and split. A heat-sealed end on a cotton cord is generally the weakest option, because cotton does not melt cleanly.
The channel itself is worth a line in the spec. Too narrow and the cord binds and will not draw. Too wide and it twists, flips over on itself and bunches. And if a cotton cord is used in a channel that does not shrink at the same rate, the cord comes back from the first wash relatively too short or too long, and the garment stops closing properly — cord and shell should be shrinkage-tested together. If the cord is dyed to match the garment, its colour fastness has to be checked with the shell, not on its own.
Also give the cord a stated length. It has to be long enough to tie comfortably with the garment closed on the largest size in the range, and short enough that the ends do not hang below the hem. This is one of the most common fit complaints on drawcord garments and it costs nothing to get right. Children’s garments have separate drawstring rules for safety reasons, covered elsewhere on this site; the notes here are about adult garments.
特定: cord construction and diameter, tip finish, cord length by size, eyelet or opening type, channel width, whether there is a bar tack or an end stopper, and colour matching.
Elastic: it does not break, it gives up
Elastic rarely snaps. It loses recovery — it still stretches, but it no longer pulls back, and the waistband or cuff goes slack. Two things cause that: the wrong elastic for the job, and damage during either sewing or wear.
Choosing the type
- Braided elastic narrows noticeably when it is stretched, and tends to roll inside a casing. It also loses recovery where a needle has pierced it. Use it inside a casing on light work, and avoid stitching directly through it.
- Knitted elastic is soft, keeps its width when stretched, and tolerates being stitched through much better. It is the usual choice where the elastic is attached directly and will sit against the skin.
- Woven elastic is the firmest. It keeps its width, resists being over-stretched, and holds its shape best under load. It is the right choice for a waistband that carries weight.
Note that this is about the trim, 生地ではありません. How a knitted shell fabric grows and recovers is a separate question with its own causes, covered elsewhere on this site.
How elastic gets damaged
At the sewing machine. Elastic that is pulled hard while it is being attached is being fatigued before the garment is even finished. It should be attached at a stated, controlled extension, with the presser foot pressure set so the feed does not stretch it further. Where elastic must be stitched through, a rounded needle point pushes the fibres aside instead of cutting them — needle and thread choice generally is covered elsewhere on this site, but for elastic this one detail is worth naming.
In wear and washing. Elastane loses its recovery permanently under heat, so hot washing, hot tumble drying and hot pressing all shorten a waistband’s life. Chlorine attacks it, which is why ordinary elastic in a swim or beach garment goes slack quickly and chlorine-resistant elastic exists. Body oils, sweat and strong detergents degrade it more slowly but in the same direction. Prolonged sunlight does too. None of this is reversible: once the fibre chemistry has broken down, no wash or treatment brings the recovery back.
Some of this is a care-label question rather than a construction one, but the choice of elastic should reflect where the garment will actually live. ビーチウェア and swim need chlorine-resistant elastic. A garment that will be tumble dried needs elastic that tolerates it.
特定: elastic type (braided, knitted or woven), 幅, the cut length or the extension ratio at which it is attached, how it is finished at the join, whether it is stitched through or enclosed, and chlorine resistance where the end use calls for it.
Three things that apply to every fastening
Approve the actual trim, not a description. A written specification tells the factory what to buy. A sealed, signed sample tells everyone what “correct” looks like when a substitution is proposed later. Keep both.
Test the fastening on the finished garment. A zip that works on a table can bind when it is set into a lined garment. A snap that holds on a scrap of shell fabric can tear out when the interlining changes. A wash test on the assembled garment catches shrinkage mismatch, colour transfer from a dyed cord or tape, and elastic that goes slack — none of which show up on the trim alone.
Say what happens when it fails. Fastenings are the parts most likely to need service. Name the slider, the snap and the button on the specification precisely enough that a replacement can be sourced, and consider supplying spare buttons with garments that carry distinctive ones.
If you are working on a garment where the fastening is doing real work and you want a view on what to specify, send us the design and the intended end use and we will go through it with you.
