Pre-Stretch Film Explained: 200% vs 300% and the Real Film Cost per Pallet

Pre-stretch is the amount a stretch film is elongated before it reaches the pallet, stated as a percentage of extra length. At 250% pre-stretch, one metre of film unwound from the roll becomes 3.5 metres of film on the load. Hand wrapping manages 10–20%; a powered pre-stretch carriage on a wrapping machine runs 200–300% all day. Because film is sold by weight, the pre-stretch figure decides film cost per pallet more than the price per kilogram does, and a plant wrapping 30 pallets a day by hand is typically using three to four times the film it needs.

The rest of this article puts numbers on that: how the percentage works, what happens to the film when it is stretched, a worked cost-per-pallet comparison in grams (not rupees, because the rate per kilogram is yours to fill in), a yield table for every gauge we make, and the cases where a thick blown film still beats a thin pre-stretched one.

What the percentage actually means

Pre-stretch percentage is the extra length, not the final length. The multiplier on film length is (1 + pre-stretch ÷ 100):

• 0% (film applied at roll length): 1 m on the roll = 1 m on the pallet.
• 15% (typical strong hand wrap): 1 m = 1.15 m.
• 100%: 1 m = 2 m.
• 200%: 1 m = 3 m.
• 250%: 1 m = 3.5 m.
• 300%: 1 m = 4 m.

The film gets proportionally thinner and narrower as it stretches. A 17 micron film at 250% is about 4.9 micron thick per layer on the pallet and has lost some width to necking, usually 10–15% on a cast film. This is not a defect: as LLDPE stretches, its polymer chains align along the machine direction, which raises tensile strength and, more importantly, reduces creep. Creep is the slow relaxation of tension that lets a hand-wrapped pallet loosen over a fortnight in a godown. Pre-stretched film has already been through most of its elongation, so what remains holds its tension.

There are three ways of getting pre-stretch, and they should not be confused. Hand pre-stretch is the operator pulling the roll against the load: 10–20% at best, inconsistent between packers and between the start and the end of a shift. Machine pre-stretch uses two rollers in the film carriage geared to run at different surface speeds; the ratio between them sets the percentage and it is the same on every pallet. Factory pre-stretched film, sold as pre-stretched or "pre-stretch" hand film, has been oriented at the film plant to 7–12 micron and is applied by hand with only a few percent of further stretch; it gives a hand-wrap operation most of the yield of a machine at the cost of a dearer film per kilogram. The pre-stretch glossary entry has the short version.

Film weight: the one formula you need

Cast LLDPE has a density of about 0.92 g/cm³, so film weight per square metre is micron × 0.92. That gives 15.6 g/m² for 17 micron, 18.4 for 20, 21.2 for 23, 23.0 for 25 and 27.6 for 30 micron. From there, the film mass on any pallet is:

Grams per pallet = applied metres ÷ (1 + pre-stretch ÷ 100) × film width (m) × g/m²

Applied metres is the length of film actually lying on the load: pallet perimeter × number of turns. Everything else in a cost-per-pallet comparison follows from this one line.

Worked example: 23 micron by hand versus 17 micron at 250%

Take a common Indian unit load: 1200 × 1000 mm pallet, load 1500 mm high, regular corrugated cartons, no sharp edges. Perimeter = 2 × (1.2 + 1.0) = 4.4 m. Wrap pattern: 3 turns at the base, a spiral up at 50% overlap (1500 ÷ 250 = 6 turns), 3 turns at the top: 12 turns of 500 mm film, so about 53 m of film on the pallet. Hold the pattern constant and vary only gauge and pre-stretch.

*Relative cost assumes the same rate per kilogram for every row; multiply the grams by your actual rate per kg for each film to get your own comparison. Weight per pallet is what to ask any supplier for; a lower price per kilogram on a heavier film is frequently the dearer option per pallet.

Read the table two ways. Moving from 23 micron hand wrap to 17 micron at 250% on a machine cuts film per pallet by about 75%, from roughly 490 g to 120 g. Moving from 200% to 300% on the same 17 micron film saves a further 25%, but you are now at 4.3 micron per layer, which is where puncture and edge-tear start to show on anything other than clean cartons. Most plants settle at 200–250% with 17 micron or 20 micron cast film for regular loads, and keep a 23 micron roll on the machine for export pallets and anything with hard corners.

Film yield by gauge: metres per kilogram

Because film is sold by net weight, yield in metres per kilogram is the quickest way to compare gauges. Figures are for 500 mm width; scale proportionally for 250, 300 or 750 mm rolls.

One kilogram of 17 micron film at 250% pre-stretch covers about 448 applied metres, which is roughly 8 pallets of the size in the worked example. The same kilogram of 23 micron applied by hand covers 108 metres, or about 2 pallets. That four-to-one ratio is the whole economic case for a wrapping machine, and for most plants wrapping more than 15–20 pallets a day the machine pays for itself in film within a year, before counting the labour saved.

Holding force: why thinner film often holds better

The natural objection is that 5 micron of film on the pallet cannot hold as well as 20 micron. It holds differently. Containment force, the inward pressure the film exerts on the load, comes from the film's tension multiplied by the number of layers. Oriented film resists further elongation, so the tension a machine sets stays put; a hand wrap starts loosening the moment the operator lets go. A machine also applies its wrap force consistently up the full height, where a hand wrap tapers off at the top corners the operator cannot reach.

The right way to specify holding is not by micron but by containment force, measured with a spring gauge pulled against the film on the loaded pallet. Typical targets are about 3–5 kgf for light, stable cartons and 6–8 kgf for heavy or unstable loads. Get there with pre-stretch, wrap force and turns, then pick the thinnest gauge that survives the load's edges. If the film is being torn by the load rather than failing on tension, that is a puncture problem and the answer is in the next section, not in more turns.

When thick blown film still wins

Cast and blown are the two ways of making stretch film, and they behave differently under pre-stretch. Cast film, which is what we manufacture, has consistent gauge, high clarity, quiet unwind and good cling; it pre-stretches smoothly and evenly, which is why it dominates machine wrapping. Blown film has a tougher, more irregular structure with higher puncture and tear resistance and higher holding force at a given gauge, at the cost of clarity, a noisier unwind and less consistent pre-stretch.

Thick blown film, 23–30 micron applied at modest pre-stretch, is still the right specification for:

• Sharp loads: fabricated steel, bare castings, brass hardware in open trays, timber with nails, anything that presents an edge to the film.
• Unstable loads with a high centre of gravity, where the film has to resist a shear it was not designed for.
• Very heavy loads, above about 1,000 kg, where the containment force needed exceeds what thin film can supply without tearing at the pallet edge.
• Multimodal export journeys with 15–25 days of vibration, where a small puncture grows into a torn band.

For those loads, the economics reverse: the cost of one collapsed pallet of machined parts exceeds a year's film saving. Use 23–30 micron, add corner boards so the film has a smooth edge to bear on, and accept the higher grams per pallet. The full comparison of hand and machine grades is in stretch film explained: hand vs machine, gauge and pre-stretch.

How to specify stretch film for pre-stretch: checklist

1. Application: hand dispenser, semi-automatic turntable, or automatic wrapper; and the machine's rated pre-stretch range if it has a powered carriage.
2. Gauge in micron and the film weight in g/m² (micron × 0.92 for cast LLDPE), so rolls can be compared on net weight.
3. Roll specification: width (500 mm standard), net film weight per roll, core diameter (76 mm) and, for machine film, maximum roll weight the carriage will take.
4. Pre-stretch you intend to run, so the supplier can confirm the film's maximum stretch before break (a good cast film should tolerate 300% on a machine with a margin).
5. Load description: carton or crate, edge sharpness, weight per pallet, height, and whether it is column or interlock stacked.
6. Journey: local delivery, domestic road, or export container, and expected storage time under wrap.
7. Cling: single-side cling standard so pallets do not stick to each other in the truck; double-side on request.
8. Target containment force, if you measure it, or the current grams of film per pallet you are trying to beat.

Point two is the one to insist on. Rolls sold by count or by gross weight, including the core, are impossible to compare; two "3 kg rolls" can carry very different amounts of film. All our film is sold on net film weight and quoted per kilogram, which is described on the stretch film glossary page.

Cutting your film cost per pallet

If you send us your pallet dimensions, load type, the wrapper you use and the gauge you are running now, we will work out grams per pallet for your current setup against two or three alternatives, and tell you whether the saving is in gauge, in pre-stretch or in a wrapping machine you do not yet have. We supply cast LLDPE in hand and machine grades from 17 to 30 micron and dispatch across India from Rajkot; details and dispatch lanes are on the stretch film manufacturers in India page.