Reference guide
Comparing Poly Mailer Materials
This guide exists because comparing two packaging quotations is harder than it should be. One supplier quotes a micron figure, another quotes mils, a third quotes neither, and the three bags in front of you feel different from all of it.
What follows is how to compare them properly: what the published numbers do and do not tell you, what to ask instead, and how to test two films against each other without laboratory equipment.
Why gauge figures rarely compare
Three reasons, and none of them is dishonesty.
The first is units. Microns and mils both describe thickness, and quotations mix them freely. Converting is easy; noticing that one supplier quoted a target and another quoted a minimum is not.
The second is what was measured. A figure taken on flat film and a figure taken on a finished bag describe different things, and the difference is not constant.
The third is that thickness alone does not determine performance. How the film was produced, what it is blended from, and how the seals were made all affect whether a bag survives a drop. Two films of identical stated thickness can behave noticeably differently.
None of that makes the number useless. It makes it insufficient on its own, which is why the questions below matter more.
What to ask instead of asking for a gauge
Five questions that reveal a genuine difference between two suppliers.
What is this film recommended for?
A supplier who answers with the contents rather than with a number is thinking about your problem.
What is the next weight up, and what does it change?
Knowing what an upgrade buys you tells you where the current specification sits.
Is the figure a target or a minimum?
A minimum is a commitment. A target is an aspiration, and the difference matters at the bottom of a run.
Was it measured on film or on the finished bag?
Ask both suppliers the same question and you will often find you were not comparing the same thing.
What is the recycled content, and what evidences it?
Feedstock type, proportion, and a document. All three, or the claim is decorative.
Testing two films against each other
No equipment needed. Do all five with the same contents, on the same day.
Pack both with your real heaviest order
Not a proxy. The thing that actually fails is the thing to test with.
Drop each once, flat, from bench height
Onto a hard floor. Then again on a corner, which is where concentrated force shows up.
Press a hard corner against the film from inside
A box corner or a buckle, with steady pressure. This is the failure mode that separates weights.
Test the seal properly
Peel, fold, press the whole length, then pull the flap firmly. A partial bond shows up immediately.
Wet the outside and leave it
Twenty minutes with water on the panel and around the closure. Check whether anything reached the contents.
What each material variable actually changes
Useful when a quotation offers options and you are deciding which are worth paying for.
| Variable | Addresses | Does not address |
|---|---|---|
| Film weight | Puncture and tear from concentrated force | Crushing, surface scratching |
| Opacity | Contents showing through | Anything structural |
| Finish | How marks and print colour read | Strength |
| Bubble lining | Impact | Crushing, abrasion |
| Foam lining | Surface abrasion | Impact from a drop |
| Gusset | Lofty contents deforming the parcel | Protection |
| Recycled content | An environmental requirement | Performance, either way |
Where the film is not the variable that matters
Buyers often arrive at a material comparison having already decided that the film is the problem, when the actual cause is fit or format. Contents moving inside an oversized bag, or a rigid item in a flexible one, will fail on any film weight you choose. Before comparing materials, it is worth confirming which failure you have, which is set out in the protective format comparison.
Questions about the material guide
How thick should a poly mailer be?
The question does not have a general answer, because thickness only matters relative to what is inside. Soft goods with no hard edges need very little; a boxed item with corners needs substantially more. Specify against contents, not against a number.
How do I compare two suppliers’ film specifications?
Ask both the same three questions: is the figure a target or a minimum, was it measured on film or on the finished bag, and what contents is it recommended for. You will often find the numbers were never comparable.
Does recycled content make a film weaker?
It can behave differently, which is why the specification should be checked against your actual contents rather than substituted like for like. Ask the supplier what changes, and test a sample before switching a live flow.