Zip-Track, Keder and Zipper Edges: How Retained-Edge Screens Hold Their Mesh
A zip-track screen has a strip of zipper teeth or a plastic bead welded along each side of the fabric, and that strip runs inside a captive channel in the side track so the fabric cannot pull out sideways. That one detail is what lets zip screens span large openings and resist wind that would blow a conventional screen out of its guides. This page explains the edge types, how they are attached, how the track holds them, and what fails.
Key takeaways
- "Zip" edges use half a zipper (teeth only, no slider) welded to the fabric; "keder" edges use a round or shaped bead. Both work by being wider than the track's slot.
- Edges are attached by high-frequency or ultrasonic welding, sometimes with stitching; adhesive-only edges are a warning sign on large screens.
- The track liner (usually a low-friction plastic insert) is a wear part and is often what makes a zip screen run quiet or noisy.
- The fabric panel, edges included, is manufactured to exact width: zip screens are not rescreened like spring screens.
- Most zip failures come from width mismatch, track misalignment or debris, not the zipper itself.
How retained edges work
In a conventional screen, the fabric edge simply sits in a channel. Wind pushes the fabric into a curve, the curve shortens the effective width, and the edge slides out of the channel. In a retained-edge screen, the edge carries something thicker than the channel's slot opening. As wind loads the fabric, the edge pulls against the slot lips and stays put. Load goes into the track, then into the building, instead of pulling the fabric loose.
This is why the zip-track design dominates large exterior screens. The wind performance side, including EN 13561 wind classes as applied to external blinds and screens, is covered in zip-track screens and wind resistance. This page focuses on the edge hardware itself.
Zipper vs keder vs hybrid edges
Zipper edges
One half of a coil or molded zipper (teeth or coil on a woven tape) is welded or sewn to each fabric edge. There is no slider and nothing to zip. The teeth form a bulky, flexible bead that rides behind the track's slot lips, often inside a plastic liner shaped to match. The teeth give good grip against the liner, and the bead flexes easily around the roller.
Keder edges
A keder is a bead: a rope, PVC rod or extruded profile enclosed in a fabric or PVC flap, welded to the screen edge. In zip screen systems, the bead runs in a round-bottomed channel. Keder edges are smooth, so they run with less friction, but they can be less tolerant of side load than zipper teeth in some designs. The same principle is used to attach awning fabric to rails; see awning keder, welt and valance rails.
Hybrid and proprietary edges
Some manufacturers use molded hook profiles, ribbed strips or combinations. These are designed together with a specific track and liner, and parts are not interchangeable between brands.
| Edge | Grip under wind load | Friction | Roll size added | Repairability |
|---|---|---|---|---|
| Zipper tape (coil or molded) | Very good | Moderate | Small, flexible | Panel replacement; some edges can be rewelded by fabricators |
| Round keder bead | Good to very good, design dependent | Low | Small to moderate | Panel replacement; bead can be replaced by a fabricator |
| Proprietary profile | Varies | Varies | Varies | Manufacturer only |
How edges are attached to the fabric
Zip screen fabrics are usually PVC-coated polyester or PVC-coated fiberglass screen and shade fabrics, specified by openness factor. The coating lets the edge be welded:
- High-frequency (HF) welding melts the PVC coating of the fabric and the edge tape together under pressure. It produces a strong, waterproof joint and is standard for PVC-coated fabrics.
- Ultrasonic welding uses vibration to generate heat locally. Common for some thermoplastic tapes and thinner fabrics.
- Hot-air or hot-wedge welding is used in some fabrication shops for long runs.
- Stitching, sometimes combined with welding, adds a mechanical backup.
Pure adhesive attachment exists on some budget products. It can creep under constant tension and heat, especially on dark fabrics in full sun. If a quote does not specify how the edges are attached, ask.
The track, liner and re-entry funnel
A zip track usually has an aluminum outer extrusion, a plastic inner liner that the edge actually slides in, and sometimes a separate retention clip. The liner reduces friction, damps noise, and can be replaced when worn. At the top of the track, a funnel or guide piece feeds the edge from the roller into the liner smoothly.
Some systems include a "self-repairing" or re-entry feature: if a strong gust or an impact pulls the edge out of the track, the edge is guided back in the next time the screen is raised and lowered. This is a real benefit on exposed sites, but it is a recovery feature, not a reason to leave a screen down in winds above its rating.
Why width tolerance matters so much
A zip screen panel is made to a precise width, edge to edge. The tracks must be installed so the distance between the liners matches that width within a tight tolerance at every point from top to bottom. Too wide and the fabric is pulled taut sideways, which increases friction, wears the edge and can tear the weld. Too narrow and the fabric bows and creases, and the edge can ride out of the liner.
Common edge failures and what causes them
| Failure | Likely cause | Remedy |
|---|---|---|
| Edge pulls out of track | Wind above rating, tracks too far apart, worn liner | Check spacing; replace liner; use wind sensor or retract earlier |
| Weld separating from fabric | Excess side tension, heat, poor weld | Panel repair or replacement by manufacturer |
| Fabric creasing near edges | Tracks too close or not parallel | Realign tracks |
| Screen jams part-way | Debris in liner, bent track, misaligned funnel | Clean liner; straighten or replace track; realign top guide |
| Uneven roll on the tube | Edges thicker than fabric, roll stacks at sides | Normal to a degree; severe cases need correct roller and fabric match |
| Squeal or chatter | Dry or dirty liner | Clean and apply dry lubricant |
If the fabric repeatedly leaves the track, start with screen off track, then check the track geometry described in screen tracks and guide rails.
Repair or replace?
Because edge, fabric and roller are matched, zip screen fabric is normally replaced as a complete panel made to the screen's exact size by the manufacturer or a certified fabricator. A local canvas or awning shop with HF welding can sometimes reweld a separated edge, but warranty coverage usually ends there. Tracks and liners are generally available as separate parts. Motors are covered in motorized patio screens.
Frequently asked questions
Can I convert a regular retractable screen to a zip screen?
Not practically. Zip retention needs welded edges, a matching track and liner, and a housing designed to feed the edges. In effect it is a new screen system.
Do zip screens keep insects out completely?
They seal the sides very well, because the edge is captive in the track. Bugs can still get in at the bottom if the bottom bar does not seal against an uneven floor, so a bottom seal or a level sill matters.
Is a keder edge the same as a zipper edge?
No. A keder is a smooth bead, a zipper edge uses teeth on a tape. Both retain the fabric, but they need different track profiles and are not interchangeable.
Why does my zip screen make a ticking sound?
Often the zipper teeth are catching on a worn or dirty liner, or on a slight step where track sections meet. Cleaning the liner and checking joints usually fixes it.
How long do zip screen edges last?
On quality PVC-coated fabrics with welded edges, edges commonly last as long as the fabric itself, often 10 years or more. Liners may need replacing sooner on dusty or sandy sites.
Can zip screens stay down in a storm?
Only within their stated wind rating. Above that, retract them, or use an automatic wind sensor on motorized systems. Retained edges reduce failures but do not make a screen storm-proof.
Sources and standards consulted
- Screen mesh specification sheets (fiberglass, aluminum, polyester and PVC-coated meshes) (manufacturer documentation)
- Spline and screen frame channel specifications (manufacturer documentation)
- Retractable screen and zip screen component catalogs (manufacturer documentation)
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