Wrapping a pallet is one operation, but the film has to perform three different tasks at once in it. It has to cling to itself so that the wrap does not unwind. At the same time it has to slip on the outer side so that pallets do not stick to each other in transport. And it has to carry the stress created when it is stretched.
These three requirements contradict each other. A material that clings well to itself slips poorly. A material optimised for strength loses cling. That is why the film is divided into layers and each one gets a single task.
Outer layer: slip
The side that is on the outside after wrapping. It must be smooth - otherwise two neighbouring pallets would stick together in transport, and during unloading the forks would tear the film off one of them. This layer is not responsible for any strength; it makes sure the pallet can be placed next to another one.
Inner layer: cling
The side that touches the load and the previous wrap. It is what makes the wrap hold by itself - without adhesive and without heat. When the operator finishes wrapping and tears off the film, the end sticks to the layer below thanks to this side.
A roll mounted on the stretch wrapper the wrong way round has the slip side inwards and the cling side outwards. The wrap then does not hold, and pallets start sticking to each other. The symptom looks like a film defect, but it is a setting error.
Load-bearing layers
Between slip and cling lies what determines strength. In standard film this is a single composition - a compromise between all three tasks. In a five-layer construction these are separate layers that no longer have to reconcile anything and can be optimised solely for carrying stress.
| Layer | Task | What happens when it fails |
|---|---|---|
| 1 · outer | slip | pallets stick to each other in transport |
| 2 · load-bearing | stress distribution | stress concentrates at one point |
| 3 · load-bearing | carrying stress | the film breaks instead of stretching |
| 4 · load-bearing | stress distribution | tearing on the load side |
| 5 · inner | cling | the wrap unwinds |
Why the pallet corner is the hardest part
On a straight side of the pallet the film works evenly - the stress is spread across the whole width of the band. At the corner the same force is concentrated on a narrow section of material, often on the sharp edge of a carton or profile.
That is why breaks almost never start in the middle of a side. They start at the corner: first a small tear, then a split along the entire wrap. The better the load-bearing layers distribute the stress away from the point of contact, the later this happens.
What this means for selection
- Regular, light loads on short routes - standard film is enough. A multi-layer construction has nothing to improve here.
- Sharp edges, heavy weight, multiple transhipments - here the difference between a single-composition film and a polymer-reinforced film is visible from the first pallet.
- Breaks despite thicker film - a sign that the problem is not the number of microns, but how the material copes with point stress.
Thickness tells you how much material there is - construction tells you what that material can do. Two films with the same number of microns can behave completely differently on a corner.