Stretch Wrap Containment Force: The Number With No Test Method

Stretch film gets bought by gauge and judged by containment force, and only one of those two numbers has an agreed definition behind it. Thickness is easy to measure and nearly useless as a predictor of whether a load arrives standing up.

Containment force answers the real question. It describes how hard the film squeezes the load together, which is what resists a corner coming loose on a trailer floor.

Buyers feel the difference in two places. Film that holds a load with less plastic costs less per pallet, and loads that arrive standing up cost nothing in claims.

The trouble starts the moment two people compare readings. Different gauges, different heights on the load and different hands produce different numbers from the same wrapped pallet, and nothing in the published standards picks a winner.

This reference covers what the number measures and why no method standardizes it. It also covers what a real specification asks for instead, where pre-stretch changes the economics, and what the load has to survive once it leaves.

What Containment Force Measures

Wrapped film behaves like a spring under tension. Containment force is the resulting squeeze, read as the pounds needed to pull the film away from the load at a chosen point.

Gauge measures something else entirely. Thickness tells you how much plastic is present, while containment force tells you how much work that plastic is doing.

The two come apart quickly in practice. A thick film applied loosely can hold a load together worse than a thin film applied under proper tension, and the thin film costs less per pallet.

Three variables set the final figure. Film tension at the roll, the number of revolutions at each height, and how much the film was pre-stretched before it reached the load all feed into it.

That is why containment force sits above gauge in any sensible specification. It is an outcome, where gauge is an input, and only the outcome tracks loads arriving intact.

Gauge still needs translating before two quotes can be compared. One gauge equals 0.01 mil and one mil equals 25.4 microns, so dividing gauge by 100 gives mils and multiplying by 25.4 gives microns.

Run the common case. An 80 gauge film is 0.8 mil, which works out near 20.3 microns, and 80 gauge is the usual starting point for ordinary pallet loads.

Mixed units are how two suppliers appear to offer different films. The sheets read differently while the plastic is the same thickness.

Nobody Standardized the Measurement

The governing document is ASTM D4649, a guide covering the selection, specification and use of stretch films for unitizing, reinforcing and palletizing.

Read its scope before leaning on it. The guide addresses indoor environments only, and explicitly does not cover outdoor exposure.

It names the places too: warehouses, closed containers such as truck trailers and rail boxcars, and transfer terminals, for storage or for transport.

It also carries a plain warning that extreme temperatures can degrade film performance. A load wrapped at room temperature and trucked through a July afternoon is outside what the guide describes.

The measurement question is where things get awkward. According to one equipment maker’s reading of the standard, its Annex A1 illustrates example tools, including a pull plate method and a wrap-in scale method.

The same reading notes the standard’s own disclaimer: those annex methods are not ASTM standards. So the figure every specification quotes has illustrations behind it rather than a method.

Four generic tool families are in use, and they differ in ease of use, consistency and accuracy. Some need a flat load face, some need a skilled operator, and some can be used anywhere on the load.

None of that makes the number useless. It makes the number local, which is a different problem and a manageable one.

The practical consequence is simple. A target is only enforceable when the tool, the measuring position and the procedure travel with it. A supplier quoting a figure measured another way is not quoting the same thing.

What a Real Specification Asks For

A published corporate packaging specification shows what a usable requirement looks like, and it is considerably more than one number.

For a stable load between 250 and 750 pounds it calls for 5 to 7 pounds of containment force at all points of the load. It names top, middle and bottom explicitly.

That phrasing does real work. A load can read 6 pounds at the middle and almost nothing at the top, which is exactly how top layers walk off in transit.

The target also scales with the load rather than sitting fixed. Four categories each carry their own range.

Load category	Weight	Containment force
Very light	Under 250 lb	2–5 lb
Stable mid-weight	250 to under 750 lb	5–7 lb
Heavy	750 to under 2,000 lb	7–12 lb
Very unstable	Over 2,000 lb	12–20 lb

From lightest to heaviest the requirement runs four to one. A plant wrapping mixed product at one machine setting is overwrapping half of it and underwrapping the rest.

Requirement	Specified value	What it prevents
Containment force	5–7 lb at top, middle and bottom	Layers shifting where the wrap went light
Wraps at top	4 revolutions	Top layer lifting or sliding
Wraps at bottom	4 around the bottom layer and pallet	Load separating from the pallet
Overlap	40–60% of film width	Gaps between film bands
Film above the load	2–6 in	An unsupported top edge
Film onto the pallet	1–2 in	The load walking off its deck
Film tail	None longer than 4 in	Snagging in conveyors and handling

Attaching the film to the pallet gets its own instruction, either between load and pallet or tied to the decking. The cable sits an inch or two down from the pallet top.

Read as a whole, the specification treats wrapping as a procedure rather than a setting. Every line is a failure mode somebody met and wrote down.

Pre-Stretch Decides the Economics

Stretch film arrives able to extend far further than anyone uses. Films commonly reach around 500 percent stretch at break, while loads get wrapped at roughly 100 to 300 percent.

Pre-stretch is where that headroom gets spent. A machine pulls the film between two rollers turning at different speeds, stretching it before it ever touches the load.

The commercial effect is large. Film stretched to 250 percent covers two and a half times the area per pound of resin, so the same containment force arrives at a fraction of the material cost.

Hand wrapping cannot do this. A person walking a pallet applies tension by drag and body weight, which stretches the film modestly and inconsistently, so hand-wrapped loads cost more per pallet and vary more.

Pushing stretch too far has its own failure. Over-stretched film loses the elastic recovery that supplies containment, and it tears at corners and edges where the load concentrates stress.

Which is why pre-stretch is a setting worth measuring rather than assuming. The number on the wrapper’s dial and the stretch actually achieved on a given film are not reliably the same.

The Other Numbers on the Spec Sheet

Film data sheets carry several headline figures, and each one has the same requirement as containment force: name the method or the number means little.

Impact resistance comes from a free-falling dart. ASTM D1709 covers the energy that causes film to fail under a dropped dart, and reports the dart mass at which half the specimens break.

Two methods exist and they are not interchangeable. Method A drops a 38.10 mm dart from 0.66 m, while Method B drops a 50.80 mm dart from 1.52 m, so the same film returns different figures.

Tear behavior uses a pendulum. ASTM D1922 measures the average force needed to propagate a tear already started, for films up to 0.25 mm thick.

Direction matters there. The standard itself notes that films often show marked anisotropy in tear resistance, so a single tear value without a stated direction is half an answer.

Number	Method	What it reports
Containment force	No method standard	Pounds, at one position, with one tool
Dart impact	ASTM D1709, Method A or B	Dart mass at 50% failure
Propagation tear	ASTM D1922, Elmendorf	Force to continue a tear, by direction
Gauge	Thickness measurement	How much resin is present

Production route shapes the trade-off as well. Cast film runs more consistently at lower cost, while blown film clings better, so the choice trades repeatability against grip.

When Film Is Not Enough

Film is one of three unitizing methods the same specification covers, and the other two take over where film runs out.

Banding

Heavy and rigid loads get straps. The specification asks for a minimum of two in each direction, with more where the application calls for it.

Placement is specific for a reason. Straps run parallel to the pallet stringers rather than across the center of a deck board, because a strap tightened over a board’s middle tends to pull the board up.

Four-way pallets carry an extra rule. The straps sit next to the bottom deck boards, placed so they cannot foul a pallet jack’s wheels.

Tubed product is called out on its own, taking two bands lengthwise plus one through the center where the package allows it.

Tension reads as a limit rather than a figure: as tight as the load will allow without damaging the product or its packaging. Powered tools follow the manufacturer’s own settings.

Material choice arrives with its reasoning attached. Polyester is preferred over polypropylene because polypropylene stretches, and steel banding is ruled out on safety grounds.

Joints take two metal clips rather than one, since a single clip can slip under load.

Edge protection

Corners need help under a drawn band. The specification calls for a laminated V-board or a plastic banding corner to carry the band across the load’s edge.

It also puts a number on how much that corner should give: an eighth to three-sixteenths of an inch of crush until the band is taut.

That tolerance is the useful part, because it tells an operator what correct looks like. The alternative is a band that has quietly cut into the top case.

Sheets between the layers

Load tie sheets do a third job, stabilizing across a layer boundary where film cannot reach. The specification sets a floor on what qualifies.

Three options clear it. The first two are at least 36-point paperboard, or at least 32 ECT C flute, which the document also states as 200 pound Mullen burst. The third is honeycomb between 0.375 and 0.5 inches thick.

Those two board figures are not a conversion of one another. Edge crush and burst describe different properties, as the ECT grade chart makes clear, so the specification names two acceptable routes rather than one value twice.

Pallet slip sheets handle the base instead. They guard against moisture coming up through the deck, nail pops and deck boards that no longer line up.

Drift, and What the Load Has to Survive

The reading is a snapshot

A containment force figure describes a wrapped load at the moment somebody measured it. Loads do not stay in that condition.

Film relaxes after wrapping. Stretched polyethylene gives back some tension over hours, so a reading at the wrapper runs higher than the same load at the dock door.

Contents settle too. Cases compress, voids close, and a load that measured well on Monday can have slack in it by the time it is loaded, especially on tall or soft-cased loads.

Temperature moves the number in both directions, which is where the guide’s indoor scope bites. Cold film stiffens and warm film relaxes, and neither case is what the specification contemplated.

Overhang deserves a check at the same time. A load wider than its pallet puts its corners past the deck edge, so the film has nothing solid to pull against at the one place it most needs purchase.

The useful response is procedural rather than numerical. Measure at a defined point in the process, record where and with what, and treat drift between wrapper and dock as information rather than noise.

What dynamic testing measures

Containment force is a proxy. What a unit load really faces is acceleration, when a driver brakes or a trailer changes lanes, and that is what dynamic stability testing measures directly.

European practice has a test method for it. EUMOS 40509 assesses load unit rigidity by applying acceleration over a period not exceeding 0.05 seconds, which simulates an impulsive event rather than a steady push.

Pass and fail turn on deformation. The method sets upper limits on both elastic and permanent deformation of the load unit, so a load that springs back still has to spring back far enough.

The acceptance figures sit inside the paid standard, so they are not reproduced here. Anyone writing them into a contract needs the controlling document rather than a summary.

Dynamic testing does not replace a containment force target. It validates one, which is the sensible relationship between a cheap daily check and an expensive annual one.

Corner protection belongs in the same conversation. Edge boards spread film tension along a load’s vertical edges, raising effective containment without adding film. They matter most on the loads least able to hold their own shape.

Common Questions