Stretch Wrap Containment Force: Testing Pallet Load Stability

The film change happens at 05:50, the wrapper's pre-stretch is nudged up to save film, and by lunchtime three pallets of bottled water are leaning against the trailer wall at a customer's dock. Every pallet looked tight when it left the wrap station. Nobody measured how hard the film was squeezing the load, and nobody had ever tested what that load needed to survive a hard stop.

Containment force is the inward force that applied stretch film exerts on a unit load. Measured the same way at the same points every shift, it turns "looks tight" into a number that a wrap recipe can be held to. On its own, though, it does not prove a load will stay square under braking; that takes a tilt or acceleration test against the forces road transport actually applies.

• What this guide covers: how containment force is measured, why the reading changes with layers, overlap and pre-stretch, how to set a site target per load class, and how to confirm it with a stability test.
• What it adds: a screening formula for restraint demand, a worked film-versus-damage cost in dollars and rupees, a timestamped wrap-station failure and a rollout checklist for DC and 3PL sites.

Containment force: the squeeze film puts on a unit load

Containment force is a measured property of the wrapped pallet, not of the film roll. Two loads wrapped from the same roll can differ by a factor of two, because the reading depends on how many layers, how much overlap and how much stretch the machine applied.

Film specifications describe the film before it meets a load: gauge, tensile strength, elongation and cling. India's product standard for this material, IS 14995:2024 (Stretch cling films, specification), is a film specification in exactly that sense. ASTM D8314 takes the other view: it is a guide to testing the mechanical properties of stretch film after a wrapper has applied it to a unit load or test structure.

• Film property: what the roll can do, set by resin, gauge and manufacturing; bought on a specification.
• Applied containment force: what the wrapped load actually feels, set by the wrapper recipe and the load's shape; measured on the floor.
• Load stability: whether the load stays within deformation limits under transport acceleration; proven by a tilt, sled or vehicle test.

The three are linked but not interchangeable. A Virginia Tech dissertation by James Bisha (2012) tried to predict applied containment force from laboratory film stiffness and found the correlation statistically significant but very weak. That result is the reason a site must measure applied force on its own loads rather than infer it from a datasheet.

Measuring containment force with a pull plate at fixed points

The common method slides a flat plate under the film, pulls it out a fixed distance and reads the force. The number is only comparable when the plate size, pull distance and position stay the same on every test.

Bisha's dissertation describes the conventional measurement as the force needed to pull a 15.2 cm plate 10.1 cm out from the load, at 25.4 cm below the top and 45.7 cm in from the side of a 121.9 cm face. Those are 6, 4, 10, 18 and 48 inches. A Virginia Tech student project used the same 10-inch and 18-inch side position and notes that the plate pull is the only containment test in ASTM D4649.

1. Wait for the film to settle: test a fixed time after wrapping, for example 10 minutes, because applied film relaxes over time and an early reading can overstate what the load keeps.
2. Mark the positions: use the same points on each face, for example top, middle and bottom on the two long faces, and record which face was the wrapper's start.
3. Insert and pull square: cut a small slit only if the method calls for it, insert the plate flat, and pull perpendicular to the face at a steady rate.
4. Read at the set distance: record the gauge value when the plate reaches the stated pull-out, not the peak during the jerk of the first movement.
5. Log the recipe: store wrapper ID, recipe number, film lot, pre-stretch setting and layer count with every reading.

Layers, overlap and pre-stretch move the reading in different ways

More layers and more overlap raise containment force; more pre-stretch tends to lower it, even though it saves film. That trade-off is why film reduction projects are the most common cause of sudden load failures.

In the Virginia Tech student project, moving from one to three layers raised corner containment by about 20 percent, and raising overlap from 29 percent to about 75 percent did much the same. Increasing the pre-stretch setting reduced containment force, which the authors put down to thinner film carrying less force. Overall stretch at the load had a small negative effect.

Park, Horvath and colleagues (2018, Packaging Technology and Science) add a second reason to care. Higher containment force changed how the packages on a pallet bridged together and improved unit-load deflection by as much as 81 percent, with the largest effect on small packages and less stiff pallets. Wrap settings therefore affect racking and stacking, not only transport.

Forces a wrapped pallet must resist on a truck

Transport rules in the US and the EU express cargo securing as fractions of the cargo's weight: 0.8 forward and 0.5 to the side and rear. A pallet in a trailer has to hold its own shape against the same accelerations that the trailer's straps or bulkheads resist.

In the US, 49 CFR 393.102(a)(1) requires cargo securement devices and systems to withstand 0.8 g deceleration forward, 0.5 g acceleration rearward and 0.5 g acceleration laterally without exceeding their breaking strength. Section 393.102(c) treats cargo as meeting the criteria if it is immobilised, for example in a sided vehicle with each article in contact with, or close to, a wall or other articles.

Pallet wrap design for road freight should be tested against the securing accelerations in 49 CFR 393.102(a)(1) and Annex III of EU Directive 2014/47/EU: 0.8 g forward and 0.5 g lateral and rearward, with load deformation kept under 10 percent elastic and 5 percent permanent in EU guidance.

The EU writes the same three values into Annex III of Directive 2014/47/EU on roadside inspection, and lists EUMOS 40509 as the applicable standard for transport packaging. Our guide to cargo securement rules for trucks covers the tiedowns and vehicle side; this article stays with the pallet itself, which those rules assume will stay in one piece.

A tilt or sled test proves stability; a gauge reading does not

The European Commission's 2014 cargo securing guidelines state plainly that a load unit's rigidity cannot be estimated by visual inspection or by measuring forces in the packaging. Containment force is a production control; a stability test is what sets the target that control enforces.

The guidelines describe three type tests. An inclination test tilts the load platform: 26.6 degrees corresponds to 0.5 g and 38.7 degrees to 0.8 g in the simple static approach of EN 12195-1. An acceleration test at pallet level holds the inertia force for at least 0.3 seconds, applied within 0.05 seconds, which is the dynamic approach of EUMOS 40509. A vehicle test drives an S-curve for 0.5 g and brakes hard for 0.8 g.

• Elastic deformation limit: measured parallel to the platform as a percentage of load height, it must stay under 10 percent during the test.
• Permanent deformation limit: after the test it must be under 5 percent of height and under 6 cm.
• Product condition: products and primary and secondary packaging must show no permanent deformation or damage.

The arithmetic of the tilt angles is simple and worth keeping on the test sheet. The static sideways component on a tilted platform is the sine of the angle, but the ratio of sideways force to normal force, which is what friction and film must resist, is the tangent: tan 26.6° is 0.50 and tan 38.7° is 0.80.

Screening estimate of film restraint needed for one layer (static approach)

  F_req = max(0, a - mu) * m * g

  a    = design acceleration as a fraction of g (0.5 lateral, 0.8 forward)
  mu   = friction coefficient between the layer and the one below it
  m    = mass of the layer and everything stacked on it, kg
  g    = 9.81 m/s^2
  F_req in newtons; 1 lbf = 4.448 N

  Tilt angle for a test:  theta = arctan(a)
      a = 0.5  -> theta = 26.6 degrees
      a = 0.8  -> theta = 38.7 degrees

Example (illustrative): top three layers of cased water, m = 300 kg,
  mu = 0.35 on unsheeted corrugated
  lateral:  (0.50 - 0.35) * 300 * 9.81 =   441 N  (about  99 lbf)
  forward:  (0.80 - 0.35) * 300 * 9.81 = 1,324 N  (about 298 lbf)

The estimate ranks recipes and shows which direction governs.
It does not replace a tilt or acceleration test: the EU guidelines note
that friction and dynamic deformation make the real demand impossible
to calculate exactly.

Turning test results into a target per load class

A workable target is the lowest containment force at which a load class passed the stability test, plus a margin for wrapper variation. Write it down per load class, not per SKU, so the floor has five numbers to hold rather than five hundred.

Group loads by how they fail rather than by what they contain: rigid cubes, compressible cases, bundled bottles, tall narrow stacks and irregular tops. For each class, wrap test pallets at three or four recipes, measure containment at the agreed points, then tilt them. The lowest recipe that passes at the governing angle sets the floor; the margin covers drift between film lots and machines.

The figures in that table are illustrative results for one hypothetical site, not recommendations. Their purpose is to show the shape of a target sheet: a measured floor, a stated margin and the extra measure each class needs when film alone is not enough.

Film cost against load damage, worked in dollars and rupees

A tighter recipe usually costs a few cents or rupees per pallet and saves far more in rejected loads. Running the numbers for one site makes the case for testing before a film-saving change, not after.

With these illustrative inputs, the tested recipe adds $2,400 or ₹1,60,000 of film a month and removes $37,800 or ₹19,80,000 of damage. The break-even is low: the extra film pays for itself once it prevents about six damaged pallets a month at the US site and about eight at the Indian site. Use your own damage and claim figures before quoting any saving.

Wrap recipe selection at a 20,000-pallet DC should weigh film against damage: in an illustrative case, adding 50 g of film per pallet costs $2,400 or ₹1,60,000 a month and pays back once six US or eight Indian damaged pallets are prevented, with recipes validated by ASTM D8314-style applied-film tests and tilt checks.

A water-pallet failure traced from wrapper to receiving dock

Most collapse claims trace back to an unrecorded settings change at the wrapper, not to the carrier. The illustrative trace below follows one shift, with document numbers, to show where a containment check would have stopped it.

1. 05:50, film change on wrapper W2: a new film lot, FL-2611-07, is loaded and the pre-stretch setting is raised from 250 to 300 percent to cut film use; no change record is raised in the maintenance system.
2. 06:10 to 07:40, 26 pallets wrapped: bottled water on licence plates LP-88410 to LP-88435 is wrapped on recipe R-14; the first-pallet containment check for the shift is skipped because the station is behind.
3. 08:05, dispatch: the pallets load into trailer TR-5531 under bill of lading BOL-70412; the yard system releases the trailer with the WMS showing every pallet as wrapped.
4. 11:20, hard braking at a signal: three top tiers slide forward on unsheeted cases; the trailer's load bar holds the pallets in position but not their shape.
5. 13:45, receiving dock: the customer records three leaning pallets and 118 crushed cases on overage, shortage and damage report OSD-3307 and raises a deduction against invoice INV-55120.

A first-pallet check after the film change would have read side containment around a third below the floor for bundled bottles and blocked the recipe until the pre-stretch was reset. That single check costs about three minutes a shift.

Which wrap checks a WMS can enforce and which need a person

Recording, comparing and blocking are machine work; judging a leaning load or a borderline tilt result is a person's call. Draw the line before buying gauges, cameras or wrapper telemetry, so each one feeds a defined decision.

Who owns the recipe, the gauge and the sign-off

Containment control fails when the film buyer, the wrapper technician and the shipping lead each assume another owns the number. Name one owner per record and one approver per change.

For 3PL sites, write the class targets and the test method into the customer's operating procedure, because a damage claim will turn on whether the agreed recipe was applied. Loads moving by sea face different accelerations, covered in our container stuffing plan guide.

Containment force control at a 3PL wrap station works when the WMS stores each pull-gauge reading against the licence plate and blocks loading below the load-class floor, with targets set by tilt tests at 26.6 and 38.7 degrees under the static method of EN 12195-1.

Rolling out containment checks across a distribution center

Start with one wrapper and the load class that causes the most claims, prove the target with a tilt test, then extend. A site can usually move from no measurement to enforced floors within a quarter.

Pallet build quality also depends on station layout and labour; see our packing station design guide, and browse the Logistics and Supply Chain hub for related warehouse methods. If you want wrap readings, recipes and claims tied together in your WMS, share your site details with us and we will scope the data and checks.