Press Seal vs Zip Lock vs Resealable Bags: What is the Difference?
Resealable is the umbrella term for any bag you can open and close again. Press seal and zip lock both describe the same interlocking rib and groove closure you press shut with your fingers, and in Australian packaging the two names are used interchangeably, with zip lock more common for heavier duty bags.
How the rib and groove closure works
Along the open edge of the bag, one wall carries a moulded rib and the facing wall a matching groove. Run your fingers along the top and the rib snaps into the groove, and the two profiles hold each other by friction and by their own shape. Pull them apart and they separate cleanly, ready to close again.
That is the whole mechanism, and it explains both the strengths and the limits. There is no adhesive to dry out and no heat needed, so the bag reseals as often as you need. But a friction fit is not a weld. A press seal closure keeps dust, moisture and fingers out, yet it is not gas tight the way a heat seal is, and a bag opened and closed hundreds of times will feel looser than a new one.
Australians also call it a click seal, zip seal or grip seal. The word zipper is borrowed from clothing and misleads: there is no slider and no teeth, just two extruded profiles.
Resealable bag ranges
The same rib and groove closure, grouped by gauge and by what the bag has to do.
So where do the names actually differ?
By convention, not by engineering. In Australian packaging the lighter gauges tend to be listed as press seal or click seal, the heavier gauges as zip lock or heavy duty zip lock, and resealable sits above both as the category name. If a supplier lists all three, they are describing the same closure at different thicknesses.
| Name | What it describes | Typical gauge | Usually used for |
|---|---|---|---|
| Resealable | The category. Any bag that opens and closes again | Any | The word you will see on a collection or category page |
| Press seal (click seal, grip seal) | The rib and groove closure, pressed shut by hand | 50µm and under | Small parts, jewellery, confectionery, samples, retail packing |
| Zip lock (zip seal) | The same closure. The name is more common on heavier bags | 75µm | Larger, heavier or sharper contents, storage, repeated handling |
| Write on panel | A press seal bag with printed white panels on the face | 50µm | Anything that has to be labelled by hand |
| Bottom loading (Maxigrip style) | Filled from the bottom, then heat sealed, and torn open at the top | 75µm | Tamper evident packs that still reseal after opening |
| Slider | A plastic slider that rides along the profile to close it | Varies | Consumer food storage, not a QIS line |
Sliders, write on panels and bottom loading bags
A slider is the small plastic clip on supermarket food storage bags. It closes the profile for you, which helps anyone with limited hand strength and makes a full-width closure easier on a large bag. It also adds cost and bulk, so it is a domestic feature more than a trade one. The QIS resealable range is press to close.
A write on panel is a band of white printing on the bag face that takes a ballpoint or marker pen. QIS write on bags carry three panels, so you can note a part number, a date and a batch without a label. It is the cheapest way to make a clear bag traceable, which is why they turn up in workshops, laboratories and anywhere stock is identified after packing.
Bottom loading bags are the one genuinely different construction. The bag is filled from the bottom and that end is heat sealed, so the closure at the top has never been opened. The customer tears the top off along side notches above the zipper, and reseals it from then on. That gives tamper evidence and a resealable pack in one, which a standard press seal bag cannot do.
What gauge changes
Gauge is film thickness, measured in microns. It changes three things at once: how well the wall resists puncture, how firmly the rib holds, and how large the bag can sensibly be made.
At 50µm the bag is light, flexible and easy to open one handed. QIS stocks that gauge from 38 x 50mm up to 125 x 205mm, the size band for small parts and retail packing. At 75µm the wall is noticeably stiffer, the rib is chunkier and takes a firmer press, and the sizes run to 380 x 510mm. That is not a coincidence: a heavy bag needs both a stronger wall and a stronger closure, which is why the big sizes only exist in the heavier gauge.
Worth knowing before you measure a sample: plastic bags are made to a nominal thickness, and QIS states a manufacturing variance of plus or minus 5 percent on size and thickness. A micrometer reading slightly under the stated gauge is normal, not a fault.
Which closure suits which job
Work from the contents, not from the name.
- Small, light, high count. Screws, beads, findings, sample sachets: 50µm press seal, smallest size that fits.
- Sharp or heavy. Hardware, tools, offcuts, anything with a corner: 75µm, and go a size up so the contents do not press on the closure.
- Has to be identified later. Write on panel, every time. A pen beats a label that peels.
- Must show if it has been opened. Bottom loading, or a heat sealed bag if it does not need to reseal at all.
- Must stay airtight. Not a resealable bag. Use a heat sealed or vacuum pouch, because a friction closure is not a gas barrier.
Australian context: food grade use and the bag bans
QIS resealable bags are described as food grade plastic, which in Australia is a statement about the material, not a certificate. There is no pre-market approval regime for food contact materials here. The obligation comes from the FSANZ Food Standards Code: Standard 3.2.2 requires packaging to be fit for its intended use and not likely to cause food contamination, and Standard 1.4.1 sets maximum levels for contaminants that could migrate into food. In practice that means keeping food packing to virgin food grade stock and not reusing a bag that has held something else.
The point almost nobody makes: resealable bags are not caught by the state plastic shopping bag bans. Those bans cover lightweight plastic shopping bags with handles, supplied to carry goods out of a shop. NSW, Victoria, Tasmania and Queensland ban them at or under 35µm, Western Australia bans all plastic shopping bags with handles regardless of thickness, South Australia bans plastic film shopping bags that are not AS-certified compostable, and the ACT has banned both lightweight and heavier boutique carry bags. A press seal storage bag has no handles and is not a checkout bag, so none of those rules apply. The bans follow the handle, not the plastic.
Resealable bags across both gauges
The same closure in 50µm and 75µm, plus write on and bottom loading versions.
Related guides
Gauge is the number that decides most of this, so start with what is a micron. The films themselves are covered in what is LDPE and what is HDPE, and the permanent alternative to a reclosable bag is explained in what is heat sealing.
The full range by size and gauge sits on resealable bags. Still deciding between 50µm and 75µm for your contents? Contact our Brisbane team on 1800 555 343 and we will talk it through.
