A winter jacket goes into a charity bag because the zip broke. Ask what broke and the answer is always the same shape: it closes, and then it opens again behind the pull, so the whole thing is finished. Nine times out of ten nothing on that jacket is finished. One stamped metal part the size of a fingernail has spread by less than a millimetre, and it is the cheapest, most replaceable component in the entire assembly.
The reason people throw out the jacket instead is that a zipper looks like one object. It is three, they wear at completely different rates, and knowing which one failed changes the repair from a new closure sewn into a coat to a two minute job at a counter.
Three parts, and only one of them does the work
A zipper is a chain, a slider, and a set of stops. The chain is the two tapes with their teeth, called elements, sewn into the garment. The stops are the small blocks at top and bottom that keep the slider on the chain. The slider is the piece you hold, and inside it are two jaws with a wedge between them.
Pulling the slider up forces the teeth from both sides around that wedge and presses them together until they interlock. Pulling it down does the reverse. The chain barely deforms during any of this. The slider does all the work, takes the full sideways force, and is the only part carrying that force every single time you use the garment, which is why it is the part that goes.
When those jaws spread, the slider still travels along the chain and still looks like it is doing its job, but it no longer squeezes the teeth deep enough to lock. So the closure zips shut and then unzips itself from below as soon as the fabric pulls sideways, usually across the chest or over a hip. That symptom, closing normally and splitting behind the pull, is the signature of a worn slider and almost never a chain problem.
The split-behind-the-pull test
Do this before you decide anything. Close the zip fully, lay the garment flat, and grip the two tapes about ten centimetres below the slider, one in each hand. Pull them gently apart, no force, the amount of tension a coat gets when you reach for a seatbelt.
If the teeth hold, your chain is sound and your slider is probably fine too. If the teeth peel open in a line and the split runs upward toward the slider, the chain is intact and the slider is not closing it properly. Now run your eye along the chain in good light and look for a gap where a tooth should be, a tooth bent out of line, or a section where the tape has frayed away from the elements. Those are the three findings that move the problem from the slider to the chain.
There is a published test method for a slider losing its grip
This failure is well enough understood to be standardised. ASTM International maintains D2061, Standard Test Methods for Strength Tests for Zippers, carried today under the designation D2061-07(2021), and the list of individual methods inside it reads like a catalogue of the ways a closure quits. Among them are holding strength of the slider lock, resistance to pull-off of the slider pull, resistance to twist of pull and slider, resistance to cushioned compression of sliders, holding strength of stops, and strength of chains and elements.
One of those methods is called slider deflection and recovery, which is exactly the property that disappears on your jacket. The standard is also explicit that no single test decides whether a zipper suits an end use, because the results are interrelated. That is the useful takeaway for a wearer: the industry treats slider deflection and chain strength as separate measurements, so you should too rather than writing off the closure as one broken thing.
France put a published price on the fix
How much this should cost is not a mystery either, because one country publishes a tariff. Under the French anti-waste law, a repair fund for clothing and shoes opened on 7 November 2023, financed by eco-contributions from brands and administered by the sector body Refashion. Consumers get the discount taken off at the till by a certified repairer rather than claiming it back.
The published amounts are specific: 7 euro off a hole, snag, or tear, 8 euro off a small zip replacement, 15 euro off a large one, 10 euro off a basic lining, and 25 euro off a multi-piece lining. The French government's own guidance for consumers adds the conditions, that the repair has to cost at least 12 euro and the discount cannot exceed 60 percent of the price. Refashion reports more than a million garments and pairs of shoes repaired under the scheme so far.
Read those numbers as a price list even if you live nowhere near France. A subsidy set at 8 euro for a small zip exists because the underlying job is small money. If a repairer quotes you a figure that sounds like a third of a new coat, you are being quoted for replacing the whole chain, and it is fair to ask whether a slider swap was considered first.
Matching the symptom to the actual part
| What it does | Likely part | Realistic remedy |
|---|---|---|
| Closes, then splits open below the pull | Slider jaws spread | New slider of the same size and type, chain untouched |
| Slider comes off the chain at the bottom | Bottom stop worn or missing | New stop, or a stitched bar tack on light chains |
| Pull tab snapped, slider still on the chain | Pull only | Replacement pull or a temporary loop through the hole |
| Jams at one point every time | Bent tooth or fabric caught in the elements | Straighten or clear the obstruction, then retest by hand |
| Gap where a tooth is missing | Chain damage | Full chain replacement, and now the larger quote is honest |
When the chain really is the problem
A slider swap cannot rescue a damaged chain, and forcing a new one onto a broken tooth line wastes the part and the visit. Missing elements mean replacement. So does a tape that has torn away from its stitching over more than a few centimetres, and so does a separating coat zip where one side has stretched noticeably longer than the other from years of loading.
Two-way zips on sleeping bags and long coats have their own version of this, since they carry two sliders and either can fail independently. Test each one separately with the same pull-apart check before you conclude anything about the chain, because a good slider at the top hides a bad one at the bottom.
What to say at the repair counter
Take the garment in closed and demonstrate the failure instead of describing it. Zip it up, pull the tapes apart, and let the person watch it split. Then ask one question: can this take a new slider, or does the chain need replacing? That single question sorts the cheap job from the expensive one in front of you rather than over the phone.
Bring the garment with you if you shop for a slider yourself, because sliders are sized and typed, coil and moulded plastic and metal chains are not interchangeable, and a number stamped on the back of the old slider tells the shop what fits. If a coat has been sitting in a bag for two winters because of this, spend one trip finding out which of the three parts actually quit. Most of the time the answer is the one that costs the least to change.