Short answer: For luggage and travel bags, use a #8 or #10 moulded plastic or metal zipper on the main opening, with lockable sliders and a two-way option on larger cases. Coil is acceptable on soft bags and internal pockets. The main opening should be rated for at least 5,000 cycles and specified with a slider that can take a padlock or a TSA lock.
Luggage is the hardest environment in the zipper world. A suitcase is overpacked, dropped, thrown onto conveyor belts, rained on and dragged by its zip. The closure is also a security feature, because the zip is often the only thing between the contents and the outside world. That combination makes the specification less about appearance and more about survival.
Detailed Explanation
The main opening takes the load. When a case is overpacked, the two tape edges are pulled apart by the contents, and the slider has to hold them together. A #5 chain will spread and the slider will jam at the corner. A #8 or #10 chain, especially a moulded or metal one, has the stiffness to resist that spread and the tooth depth to keep the slider engaged.
Two-way zips are standard on medium and large cases. They let the case be opened at one end while standing upright, which is how most travellers actually use a suitcase. A two-way also distributes the opening load across two sliders, so a single slider is not asked to hold the entire contents at one point.
Lockable sliders are a separate specification. The pull must have a loop or a hole that accepts a padlock or a TSA-approved lock, and the two sliders must be able to be locked together at the centre. This is why the pulls on luggage are larger and flatter than on garments: they have to meet in the middle and present a locking point.
Abrasion and weather follow. A suitcase zip rubs against conveyor belts, taxi floors and other bags, so the tape and the teeth must resist abrasion. Water resistance matters for soft bags and for the main opening of a case left on a wet apron. A coated tape and a storm flap are common on premium luggage.
Comparison
| Option | Strength | Abrasion | Weight | Best for |
|---|---|---|---|---|
| #10 moulded two-way | Very high | High | Heavy | Hard-shell and large cases |
| #8 moulded two-way | High | High | Medium | Medium cases, duffels |
| #10 metal | Very high | High | Very heavy | Premium and heritage cases |
| #8 coil | Moderate | Medium | Light | Soft bags, backpacks |
| #5 coil | Low | Low | Light | Internal pockets only |
The table explains why hard-shell cases almost always use #8 or #10 moulded chains. The stiffness is not for looks; it is what stops the chain spreading when the case is full.
How to Choose
Size the main opening for the packed volume, not the empty case. A 40 litre case that is routinely overpacked needs #10, while a 25 litre carry-on can use #8. Internal pockets and packing cubes can use #5 coil, because they are opened occasionally and carry little load.
Specify two-way on anything larger than a cabin bag, and lockable pulls on the main opening. Check that the pulls align when the sliders meet, because a lock needs both pulls in the same plane. Confirm the cycle rating with the supplier; 5,000 cycles is a reasonable minimum, and premium luggage often specifies 10,000.
Consider the corner radius. A tight corner puts a bending load on the tape and is where most luggage zips fail. If the design has a sharp corner, use a larger chain and a longer radius, or move the corner away from the slider park position. Donglong Zipper tests luggage chains for abrasion and cycle life and can advise on corner geometry.
Common Mistakes
Using #5 coil on a main compartment is the classic cost-down error; the chain spreads under a full load and the slider separates at the airport. The second is fitting a two-way zip without lockable pulls, which defeats the security purpose. The third is ignoring the corner radius, so the tape breaks at the tightest bend.
Designers also forget the rain. An uncoated tape on a soft travel bag wicks water into the contents. Finally, cheap sliders with soft springs lose their grip after a few hundred cycles, long before the chain is worn.
FAQ Summary
- Main opening: #8 or #10 moulded or metal.
- Two-way on medium and large cases.
- Lockable pulls that meet at the centre.
- Minimum 5,000 cycles; 10,000 for premium.
- Avoid tight corners and #5 coil on main compartments.
Luggage zips are judged in the worst week of the year, not in the shop. Specifying a larger chain, a two-way slider and a lockable pull costs a little more and removes the failures that generate returns and damaged-goods claims.