Flow Wrap Film: Choosing Film for Horizontal Flow Wrappers

Leaks waste product; registration drift can misplace the cut and reject printed packs. Choose heat seal or cold seal against product heat tolerance and the wrapper configuration, then verify film surfaces, sealing and tracking at the intended speed. This page covers the specification and fault records. The pack style itself is covered in flow wrap packaging.

What is flow wrap film?

Flow wrapping (horizontal form-fill-seal, often called HFFS) feeds products on a conveyor into a forming box where the film wraps around them. Rotating fin wheels pull the film and press the longitudinal seal, then crimp jaws make the end seals and cut. Films for flow wrapping machines are supplied as reels and are typically printed with a registration mark so the cut lands in the right place relative to the artwork.

The film has to slide over the forming box without scuffing, grip the fin wheels without slipping, seal in a short dwell time, and hold up through handling. That is why flow wrapper film is often a laminate or a coextruded film with a sealant layer chosen for the machine.

Common flow wrap film structures

Structures vary by product, barrier need and machine. These are the most common, though exact constructions differ by supplier.

Material background is in BOPP film and PET film. For product examples, see bakery packaging and pharmaceutical flow wrap.

Which layer of a flow wrap film does which job?

The table separates five jobs: outer surface and print, barrier, sealing, interlayer bonding, and slip/static control. Several layers or coatings can share a job. When a spec is written or a fault appears, start with the layer that owns that job.

Two things follow from this table.

First, some properties belong to more than one layer. Friction depends on the surface layers and on slip additives that migrate over time and can transfer from the inside face to the outside face on the roll, as explained in coefficient of friction. A new sealant grade can therefore change how the film runs over the forming box even when the print web is unchanged. On a lap seal the sealant has to bond to the outer surface, so the outer web shares the sealing job too.

Second, swapping a layer for one job can disturb another. Replacing a metallized web with clear film to show the product removes light barrier and also changes the background the photo eye reads the mark against. Moving barrier from foil to a coating or to EVOH changes how the structure behaves at creases and seals. Metallized film and EVOH film cover those trade-offs, and CPP film compares the common sealant choices. The way the layers are joined is described in laminated packaging.

Cold seal vs heat seal

Heat seal films use a sealant that softens under jaw heat. Cold seal films use a cohesive coating designed to seal to itself under pressure; confirm the coating pattern and jaw configuration for the product.

Check that your machine is configured for the system you intend to use. A cold-seal film will not run on a heated setup without changes, and the reverse is also true.

Film thickness

Specify total and layer thickness from the candidate structure’s data sheet, then confirm handling and sealing on the actual wrapper. Compare changes in gauge with tracking, wrinkles and seal results rather than assuming a thicker web runs better.

Coefficient of friction

Coefficient of friction (COF), measured in the lab per ASTM D1894, describes how easily the film slides over a surface. A flow wrapper cares about two kinds: film to metal, because the film slides over the forming box and guide rollers, and film to film, because it affects how the lap or fin lies and how the roll behaves on unwind.

• Too high a COF on metal drags the film, causing wrinkles, tension spikes, tracking drift and jams at the forming box.
• Too low a COF on the fin wheels or product contact points can cause slipping, so the film does not advance cleanly.
• Static can raise apparent friction and cause film to cling to the box or attract dust.

Slip additives bloom to the surface over time, so COF measured fresh from the converter may differ from COF after weeks in storage or after the film warms on the machine. Ask for a COF range at the end of shelf life as well as at manufacture.

Sealing performance

Fin seal vs lap seal

A fin seal joins the two inner surfaces face-to-face and folds the seam flat or out. It needs sealant on the inside only and is common on sealed packs. A lap seal overlaps the outer film over the inner and needs sealant to bond to the print or outer layer, so structure and surface chemistry must allow that. Lap seals use less film and give a flat back, but they limit structure choice.

Crimp jaws: temperature, dwell and pressure

The end seals are made by crimp jaws, typically with a serrated pattern. The three variables are temperature, dwell time (set indirectly by speed) and pressure. Seal window width, discussed in seal initiation temperature, tells you how far you can move these before the seal fails or the film distorts. A wide window is more forgiving at speed.

Hot tack and contamination

At end seals the product is often still moving and the pack is pulled while the seal is warm, so hot tack (see ASTM F1921) affects whether the seal holds immediately after the jaws open. Products that shed crumbs, oil or powder into the seal area need sealants rated for seal-through-contamination, otherwise leak rates rise even if jaw settings look correct.

Print registration and eye marks

A photo eye reads a printed registration mark and tells the machine where to cut. The mark should have strong contrast against its background, be positioned in the clear area the sensor can see, and be consistent in spacing. Registration drift commonly comes from film stretch, mark placement that varies across the roll, or low contrast on metallized or dark backgrounds. Specify mark size, position and color in the purchase spec, and check them on every new artwork.

Film tracking and tension

A wrapper needs the film to track straight. Roll quality (even winding, no telescoping), correct unwind tension and clean guide rollers all contribute. Tension that is too high stretches the film and shifts print registration. Tension that is too low causes wander and wrinkles. Check unwind brake or dancer settings when changing film, since a different stiffness or thickness shifts the best setting.

Machine speed

Speed raises the demands on every item above. At higher speed, dwell time falls, friction heat rises, static builds and the seal has less time to form and cool. A film that runs well at moderate speed may fail near the machine’s limit. Trial at the speed you plan to run, which may differ from the speed that is convenient for the first sample.

Common problems and likely causes

Leaking seals, wrinkles or drifting print: check the film or the machine first?

Start with what changed last. If the fault began with a new roll, lot or structure while machine settings stayed the same, suspect the film first. If it began after a changeover, cleaning, jaw or belt work, or it shows up on every film you run, suspect the machine first. The table gives first checks for leaking seals, wrinkles and registration drift.

Use this diagnostic sequence under the machine’s operating instructions: retained good roll at the same settings → actual jaw temperature against setpoint → product or residue at the seal → the symptom-specific alignment/sensor checks above. A fault following the roll suggests a film investigation; a persistent fault keeps the machine/setup investigation open. This is an editorial comparison sequence, not a conclusive test of cause. Enter each step in the fault record.

Fault record

This order does not hold in every case:

• If the film and the machine setup changed at the same time, for example a new structure launched on a newly adjusted line, neither can be cleared alone. Trial the film at target speed with both suppliers’ data in hand.
• With cold-seal film, check the age and storage temperature of the roll before the jaws, since the cohesive coating can block or degrade in storage.
• If the room’s temperature or humidity is outside what the machine was specified for, fix that before blaming either side. Static and friction both shift with conditions.
• Hot tack problems show up only while the pack is still warm and moving. A seal that tests fine on the bench can still open on the line, so check end seals as packs leave the jaws.

What to put in a flow wrap film specification

• Define the product: weight, shape, sharp edges, fat or dust, temperature sensitivity.
• Choose heat seal or cold seal based on product heat tolerance and machine setup.
• Set barrier needs for shelf life and confirm the structure supplies them.
• Specify COF film-to-metal and film-to-film with test method and conditions.
• Ask for seal window data and hot tack for the actual sealant, not a generic one.
• Define registration mark size, position and contrast.
• Specify core, roll diameter, weight, unwind direction and splice limits.
• Trial a full roll at target speed.

Questions for the wrapper supplier

Before the first order, confirm with the wrapper supplier:

• the minimum and maximum film width and roll size, and the core size
• the forming box size range for your product
• the jaw type and temperature range
• whether the machine is configured for heat seal, cold seal or both
• the photo eye type and mark requirements
• any film structures or thickness ranges they have tested

Wider coverage is in packaging film and machine compatibility, and the first-order risk checklist shows how supplier trials fit into a purchase.

Sources and method

Compiled from public manufacturer guidance, not our trials. The five-job table is an editorial specification framework; confirm its material choices with the candidate data sheet. Sources checked 8 October 2026:

The VFFS checks are editorial extrapolations to comparable sensors, surfaces and temperature controls. Forming-collar settings, jaw timings and numerical ranges are not transferred to a flow wrapper.