Choosing a zip can become confusing surprisingly quickly. One listing describes a metal zip, another an invisible zip, another an open-end zip and another a number 5. These terms describe different parts of the decision. A zip can be classified by its chain construction, the way its ends open, its size and the type of slider or installation it uses. “Metal” describes the material of the elements. “Invisible” describes a concealed form of coil zip.
Understanding these distinctions makes it easier to compare products and choose suitable hardware for a garment, cushion, pouch or bag. They also matter when shortening a zip, because coil, plastic-moulded and metal chains require different preparation.
Anatomy of a Zip
Most zips share the same basic structure. Two strips of zip tape carry rows of interlocking elements, commonly called teeth. When the two rows are joined, they form the chain. The slider moves along the chain to engage or separate the elements. These terms help when reading a pattern, buying components or identifying a damaged part. For other construction terms you might encounter, see my sewing terminology guide for beginners.
Tape, Elements and Chain
The tape is the fabric strip sewn into the project. It is often polyester, although cotton and specialist tapes are also available. It extends beyond the working chain at the top and bottom, providing room for handling and construction. The length of these extensions varies between products.
The elements are the parts that interlock. On a coil zip, each row consists of a continuous monofilament coil. On a plastic-moulded zip, individual plastic elements are moulded directly onto the tape. On a metal zip, individual metal elements are attached to the tape.
When the two rows are engaged, the joined section is called the chain. Its closed width is the basis for the familiar zip size or gauge numbers.
Slider and Pull Tab
The slider guides the two sides together or apart. The pull tab, sometimes called a puller, is the part you hold to move it. The slider must match both the construction and size of the chain. A slider intended for a number 5 coil chain is not automatically compatible with a number 5 plastic-moulded or metal chain. Product systems can also differ within the same category, so buy the slider specified for that exact chain.
Sliders have different functions. A locking slider is designed to resist movement when the pull is released. A non-locking slider moves more freely and is often used for bags, luggage and other applications where easy operation is useful. Some sliders have one pull tab; others have two, allowing access from either side of the project.
Top Stops and Bottom Components
The top stops prevent the slider from leaving the chain at the top. A closed-end zip has a bottom stop that keeps the two sides joined at the lower end. An open-end or separating zip uses different bottom components. One side has an insertion pin, which passes through the slider and into a retaining box, also called a starter box, on the opposite side. This allows the two halves to separate completely. These components determine how the zip functions and how it can be altered. Check their purpose before cutting or removing them.
The Three Main Zip Constructions
Start by identifying the chain. The three main construction groups are coil, plastic moulded and metal.
Coil Zips
A coil zip uses a continuous monofilament coil attached to each tape. Depending on the product, the coil may be sewn onto the tape or incorporated during manufacture. It is flexible and usually lighter than a moulded or metal chain of comparable size. Coil zips are sometimes sold as nylon zips, but many modern products use polyester monofilament. Coil zip is the clearer term when you need to identify the construction.
Their flexibility makes coil zips useful for garments, cushions, pouches, internal bag pockets and some larger bags or cases. They are available in light garment sizes and heavier ranges. Suitability depends on the gauge, tape, slider and intended load. Some coil zips show the coil on the front. Others are designed for reverse use, with the coil facing inside the project and the flatter tape side visible outside.
Plastic-Moulded Zips
A plastic-moulded zip has individual plastic elements formed directly onto the tape. These give the chain a more structured appearance than a coil. The elements are often made from POM resin. Plastic-moulded zips are available in closed-end, separating and two-way configurations and are commonly used for jackets, fleece, sportswear, bags and selected outdoor projects.
The word plastic needs care because coil elements are also synthetic. Here, plastic-moulded zip means a chain with individual moulded elements. These elements may be lighter than a visually similar metal chain and are available in many colours. Check the complete specification: a small garment zip and a large bag zip can share a construction while being designed for different levels of use.
Metal Zips
A metal zip has individual metal elements attached to the tape. Brass and aluminium are common, with different finishes available. Metal zips are used in jeans, trousers, jackets, purses, pouches and bags. Their exposed elements can become part of the design, particularly when the finish coordinates with rivets, buckles or other hardware.
Metal does not automatically mean a more suitable or stronger zip. Element size, tape, slider, end components and construction quality all matter. A larger coil or plastic-moulded system may suit a particular bag better than a small metal zip. Metal teeth also affect sewing and shortening. Keep them clear of the sewing-machine needle and prepare a tooth-free cutting and stitching area where required.
Where Invisible and Reversed-Coil Zips Fit
An invisible zip is a type of coil zip designed so that the chain sits behind a fold in the tape. When installed correctly, the seam conceals the chain and only the small pull remains visible. Invisible zips are commonly used in dresses, skirts and other garments where the closure should be discreet. An invisible-zip foot helps move the coil away from the stitching path during installation.
A reversed-coil zip also places the coil towards the inside, but it is not necessarily intended to disappear within a garment seam. Its flatter reverse side may be used as the visible face in bags, pockets, sportswear and outdoor products. Some reversed-coil products have coatings or specialist finishes.
“Invisible” describes a particular concealed zip design and installation. “Reversed coil” describes the orientation of the chain. They can look similar in a photograph, so check the product description before substituting one for the other.
Closed-End, Open-End and Two-Way Zips
After identifying the chain construction, check how the ends and sliders function. These determine whether the two sides remain joined and where the opening can be positioned.
| Configuration | How it works | Common examples |
|---|---|---|
| Closed end | A bottom stop keeps both sides joined | Skirts, trousers, pockets, cushions, pouches and many bags |
| Open end or separating | An insertion pin and retaining box allow the two sides to separate | Jackets and other full front openings |
| Two-way open end | Two sliders allow opening from the bottom or top, and the zip can separate | Long coats and selected jackets |
| Two-way closed end, O type | Two sliders face towards one another | Bags, suitcases and cases opened from the centre |
| Two-way closed end, X type | Two sliders face away from one another | Selected covers, folders and access panels |
Closed-End Zips
On a closed-end zip, the two tapes remain connected at the bottom. This is the usual configuration for a trouser fly, skirt opening, cushion, pouch or pocket. It may have one slider or, in some bag and case applications, two. Patterns that enclose both ends inside seams often use a closed-end zip or continuous chain prepared for that construction.
Open-End or Separating Zips
An open-end zip separates completely. The insertion pin, retaining box and compatible slider work together, so the bottom assembly is an essential part of the zip. This configuration is familiar on jackets. It can also be used for detachable panels, covers and other projects that need to open into two separate halves.
Two-Way Zips
“Two-way” indicates that the zip uses two sliders, but it does not describe one single arrangement. On a long coat, a two-way separating zip can open from the bottom while the top stays closed, providing more room for sitting or walking. On a bag, two sliders may face each other so the opening can be positioned along the chain.
Check the slider arrangement and end components before buying. The words “two-way” alone do not tell you exactly how the zip opens.
Continuous Chain or Zip Tape by the Metre
Continuous chain is a supply format: it is sold without the complete end components of a finished zip and cut to the required length. It is useful for cushions, pouches, bags, luggage and long custom openings. Sliders are often bought separately and must match the exact chain type and size. Some suppliers also sell continuous chain with sliders included.
Continuous chain cannot simply be converted into every finished configuration. The insertion pin and retaining box of a separating zip are specialised components, so ordinary continuous chain is not a straightforward substitute for a jacket zip.
What Zip Sizes and Gauge Numbers Mean
Zip sizes are commonly written as #3, #5, #8 or #10. The number relates to the width of the closed chain. Within a manufacturer’s system, a larger number indicates a wider chain. Treat the number as a size designation rather than an exact universal measurement. Closed widths can vary between manufacturers, constructions and product lines. Matching numbers also do not establish slider compatibility across different chain types.
For a new project, follow the pattern specification and supplier’s information. When replacing a slider, identify the chain construction and product size. Measuring the closed chain can provide an initial guide, but confirm compatibility before buying components.
Common examples include:
- #3: lighter garments, small pockets and lightweight projects.
- #5: garments, cushions, pouches, bags and jackets, depending on construction.
- #8 and #10: heavier bags, luggage, covers and selected outdoor equipment.
These are broad examples. A pattern or specialist supplier may specify another size or a product designed for a particular use.
How to Choose a Zip for Your Project
Choose a zip whose construction, function, size and appearance suit the fabric and the way the opening will be used. Start with the pattern’s hardware list. It may specify length, chain construction, gauge and whether the zip needs to be closed-end or separating. If it simply asks for a “20 cm zip”, examine the finished opening and installation instructions before choosing.
Dresses, Skirts and Concealed Garment Openings
An invisible coil zip is a common choice when the closure should disappear into a seam. It suits many dresses, skirts and fitted openings where the fabric and construction support that installation. A conventional light coil or metal zip may be specified for a lapped, centred or fly-front application. Follow the intended installation instead of substituting based on length alone.
Trousers, Jeans and Fitted Garments
Trousers and jeans often use a short closed-end zip. Metal is familiar in denim, while coil and other product-specific options appear in lighter garments. The slider function matters because the opening experiences movement and tension. Choose a product intended for the garment and follow the pattern’s specification.
Cushions and Home-Sewing Projects
Coil zips suit many cushion covers because they are flexible and available as finished zips or continuous chain. An invisible zip can create a discreet closure when the construction allows it. Removable upholstery, outdoor covers and long openings may require a larger or more specialised product. Check the intended application instead of choosing by gauge alone.
Pouches and Lightweight Bags
Coil zips are useful in many pouches because they are flexible, widely available and offered in a range of colours. A finished closed-end zip or continuous chain can work, depending on how the ends are enclosed.
Metal zips add a defined hardware detail, while plastic-moulded zips create a bolder chain. Consider the bulk where the zip meets seams, tabs or binding. A large chain can overwhelm a small pouch and make its ends harder to sew neatly. A fine garment zip may be unsuitable for a bag that carries weight and receives frequent handling.
Jackets and Separating Openings
A jacket normally needs an open-end zip so its fronts can separate. Coil, plastic-moulded and metal versions are available, with the choice depending on garment weight, design and intended use. Long coats may use a two-way separating zip to let the wearer open the lower section while keeping the top closed.
Larger Bags, Luggage and Outdoor Projects
Larger bags and luggage often use wider coil or plastic-moulded chains, frequently with two sliders. Metal can be appropriate where the product is designed for that use. Outdoor and marine projects may introduce requirements involving sunlight, salt water, abrasion or coated tape. Follow the manufacturer’s application guidance when those conditions matter.
What to Do If the Zip Is Too Long
Many closed-end zips and continuous chains can be prepared to a shorter length. The method depends on the chain construction and which original components need to remain.
A coil can be secured and cut differently from a chain with individual moulded elements. Metal zips need a clear cutting and stitching path without teeth in the way. Separating zips have a bottom assembly that must remain functional. Once you have identified the construction and end configuration, use my guide to shortening coil, plastic-moulded and metal zips.
Keep Your Zip and Project Details Together
Before buying, record the chain construction, end configuration, gauge and length. If you are using continuous chain, include the compatible slider details and how the ends will be finished.
My free Sewing Project Planner Pages give you a place to keep those specifications alongside your project notes. Recording what you used also helps when replacing hardware or repeating a make.
Get the Free Sewing Project Planner Pages
If fitting zips is your next skill to practise, my roadmap to basic sewing techniques and finishes can help you plan what to learn next.
