Price per kilogram is the wrong number
Two stretch films quoted at the same price per kilogram can differ by 40% in cost per wrapped pallet, because the film that stretches further and survives corners needs less material per load. Buyers who compare only weight end up paying for resin they never use.
Four variables decide what a roll actually delivers: the resin system, the gauge, the pre-stretch ratio the film tolerates, and the cling/slip balance. Everything else — core size, roll length, cast versus blown — is downstream of those four.
Resin: conventional LLDPE versus metallocene
Stretch film is built on linear low-density polyethylene, but the comonomer decides the mechanical profile. Butene-based LLDPE is the commodity baseline. Hexene and octene metallocene grades (mLLDPE) put the short-chain branches in a narrower distribution, which buys puncture resistance and tear strength at the same thickness.
| Property | LLDPE (butene) | mLLDPE (hexene) | mLLDPE (octene) |
|---|---|---|---|
| Puncture resistance | Baseline | +30–50% | +50–80% |
| Tear strength (MD) | Moderate | Good | Best |
| Downgauging headroom | Limited | 15–25% | 20–35% |
| Relative resin cost | Lowest | Mid | Highest |
| Typical use | Hand film, light loads | Machine film, general | Thin machine film, sharp loads |
A common compromise is a three-layer co-extrusion: mLLDPE skins for toughness, a conventional LLDPE core for stiffness and cost, with cling and slip additives dosed into the layer that touches itself rather than the whole structure.
Cling and slip are separate problems
Cling makes the film stick to itself; slip lets it unwind. Both come from additives that migrate to the surface, and they fight each other.
- One-side cling is standard for machine film. The cling layer faces inward on the roll, so the outside of the wrap stays clean and pallets do not stick together in a truck.
- Two-side cling is standard for hand film, where the operator needs the film to hold without a dispenser.
- Slip (erucamide) controls unwind force. Too little and the roll blocks or squeals at speed; too much and the wrap telescopes and the load shifts.
Ask for the coefficient of friction (ASTM D1894) rather than accepting "good cling". Machine film usually runs 0.6–0.9 film-to-film COF on the cling side.
Cast versus blown
| Cast film | Blown film | |
|---|---|---|
| Clarity and gloss | High | Lower, hazier |
| Unwind noise | Quiet | Louder |
| Tear and puncture balance | Directional, weaker in MD | More balanced |
| Minimum practical gauge | Lower | Higher |
| Best fit | Retail-ready pallets, high-speed lines | Heavy, sharp or irregular loads |
Cast film is quenched on a chill roll, which gives the optical quality and thin gauges that e-commerce and retail supply chains want. Blown film is biaxially oriented by the bubble, so it resists puncture from pallet corners and strapping.
Gauge, and what downgauging really requires
Gauge is quoted in microns (µm) internationally and in mils in North America; 1 mil is 25.4 µm. Typical working ranges:
- Hand film: 17–23 µm
- Machine film: 12–23 µm
- Pre-stretched film: supplied at 8–12 µm after mill pre-stretch
A machine film running at 250% pre-stretch turns a 20 µm roll into an effective 5.7 µm at the load. That is where the savings live, and it is also where failures come from: downgauging without moving to mLLDPE just moves the cost from film to damaged loads.
Nominal gauge is not enough. Film is sold on nominal thickness with a tolerance that is often ±5%, and profile variation across the web matters more than the average. Request the measured thickness profile, not the label.
Pre-stretch ratio and containment force
Pre-stretch is the ratio between film speed at the roll and film speed at the load. Most machine films are engineered for 200–300%, and a well-set wrapper holds that window with a powered pre-stretch roller rather than by braking.
Containment force is the number that actually predicts whether a pallet arrives intact, and it is measured rather than estimated. EUMOS 40509 has become the reference method in European road transport; ASTM D4649 covers film selection and use. A practical target for a 1,000 kg mixed pallet is enough containment to survive a 0.5 g deceleration without layer shift, verified by a tilt or horizontal force test rather than by feel.
Test methods worth putting in the purchase order
| Test | Method | What it tells you |
|---|---|---|
| Tensile strength and elongation | ASTM D882 | Base mechanical grade, MD vs TD |
| Tear resistance | ASTM D1922 | Corner and edge survival |
| Dart impact | ASTM D1709 | Resistance to sharp protrusions |
| Probe puncture | ASTM D5748 | The closest lab proxy for pallet corners |
| Elastic recovery and stress retention | ASTM D5459 | Whether the wrap stays tight after 24 h |
| Coefficient of friction | ASTM D1894 | Unwind behaviour and cling level |
| Haze and gloss | ASTM D1003 / D2457 | Retail presentation |
A supplier who can send D5748 and D5459 data for the exact gauge being quoted is a different class of supplier from one who sends a brochure.
Roll length, core and splicing
Roll length is not a fixed property — it is a function of outer diameter, core diameter and thickness:
Length ≈ π × (OD² − ID²) / (4 × thickness)
For a 250 mm outer diameter roll on a 76 mm (3 inch) core at 20 µm, that works out near 2,050 m. The same outer diameter at 12 µm carries roughly 3,400 m. Two rolls of identical diameter can therefore differ by 65% in material, which is why comparing rolls by diameter or by weight alone misleads.
Core options are 76 mm (3 inch, machine standard) and 50 mm (2 inch, hand film). Confirm splice policy: a jumbo roll with four splices per roll creates four stoppages on an automatic wrapper.
Field failures and what they usually mean
| Symptom | Usual cause | Fix |
|---|---|---|
| Film punctures at pallet corners | Gauge too low for the load, cast film on a sharp edge | Move to blown or mLLDPE, add corner boards |
| Load shifts in transit | Containment force below the transport requirement | Raise pre-stretch and overlap, verify by test |
| Film breaks at the unwind | Slip/cling imbalance, cold warehouse | Re-specify COF, store above 5 °C |
| Wrap telescopes on the roll | Winding tension too low, excess slip | Supplier winding control, lower slip |
| Film cloudy on retail pallets | Blown film on a retail program | Switch to cast |
Cost per pallet, worked through
Film weight per pallet equals wrapped area × thickness × density, with LLDPE at about 0.92 g/cm³. Wrapping a 1.2 m × 1.0 m × 1.5 m pallet with 12 m² of overlap-adjusted film at 20 µm consumes about 220 g. At 12 µm with the same coverage it is about 130 g — a 40% material reduction that only holds if the thinner film passes the same puncture test.
That arithmetic, not the price list, is what a sourcing decision should be built on.
RFQ checklist
- Gauge in microns with the tolerance you will accept, and a measured profile on request
- Resin system: conventional LLDPE or mLLDPE, and the percentage of metallocene in the structure
- Cast or blown, and the layer structure if co-extruded
- Cling side and cling level, plus COF target
- Machine pre-stretch window the film is designed for
- Roll length, core diameter, splice count per roll
- Containment force target and the test method used to prove it
- Test reports for D882, D1922, D5748 and D5459 on the quoted gauge
- Post-consumer recycled content option, if the program requires it
- Food-contact statement when film touches primary packaging
Related product categories
The materials and part types discussed above are grouped in our sourcing directory:
Standards referenced
- ASTM D882 — tensile properties of thin plastic sheeting
- ASTM D1709 — dart drop impact resistance
- ASTM D1922 — propagation tear resistance
- ASTM D5459 — machine direction elastic recovery and stress retention
- ASTM D5748 — probe puncture resistance of stretch wrap film
- ASTM D4649 — guide for selection and use of stretch wrap films
- EUMOS 40509 — load unit stability testing in transport
