Why do FFS bags split after several weeks in storage?

Delayed splitting has different mechanics from splitting during filling. The three most common causes are: environmental stress cracking (ESC) caused by contact between the film and surfactants, detergents or oils under constant stack stress; creep of the film under the load of pallets stacked several layers high; and product dust drawn into the seal area by static electricity, forming micro-channels that open after weeks. Diagnosis starts with the location of the split and a cross-section of the seal, not with increasing film thickness.

An FFS bag (Form-Fill-Seal: forming, filling, sealing) is produced directly on an automated packaging line from flat tubular film fed off a reel. The machine forms the bag, fills it with a measured dose of product and seals it, at outputs of up to 2000 bags per hour. The technology is used for bulk, granulated and powdered products in portions of 15 to 50 kg.

Which industries use FFS bags?

The largest user is the chemical and petrochemical industry (polymer granulates, fertilizers, road salt). FFS bags are also used in agriculture and animal feed production (feed, seed, growing media), in construction (cement, mortars, aggregates) and in the food industry (sugar, salt, flour, milk powder), where the film must carry documented compliance with Regulations 1935/2004 and 10/2011.

Can FFS bags be printed?

Yes. Flexographic printing in up to 10 colors turns an FFS bag into consumer packaging and a brand carrier without degrading the mechanical properties of the film. The condition is selecting inks and varnishes resistant to abrasion in transport, moisture and UV exposure in outdoor storage, which is why print should form part of the same technical specification as the film.

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FFS Bags

25 July 2026

Stop Buying FFS Film Off a Price List: An Engineering Approach

The complaint usually arrives after three weeks. The bags came off the line sealed, passed inspection and survived transport without losses. Now they are lying split open on a pallet at the customer’s site and nobody can say why. The machine? The film? The warehouse? In our experience this scenario almost always ends with the same conclusion: the film was bought from a price list rather than engineered for the application. Below we take FFS technology apart: how it works, how a film for fertilizers differs from a film for cement, and how to recognize a supplier who understands your process.

How FFS works and why it is replacing pre-made bags

FFS bags (Form-Fill-Seal: forming, filling, sealing) are now the standard for packing bulk, granulated and powdered products, typically in portions of 15 to 50 kg. The entire operation happens on a single, fully automated line. Three movements, one cycle:

01 · Form

The machine forms the bag from flat tubular film fed off a reel.

02 · Fill

A measured dose of product enters the bag without operator involvement.

03 · Seal

The top seal closes the bag. Up to 2000 units per hour.

The difference against traditional packing is easy to calculate. Pre-made empty bags have to be purchased, transported, stored and fed manually or semi-automatically. FFS tubular film arrives as a reel, takes up a fraction of the warehouse space and allows packing with minimal operator involvement. On three-shift operation this difference shows up in the unit cost of packaging faster than most companies assume in their calculations.

There is one catch. The entire output of an FFS line hangs on a single material: the film. The wrong tubing stops the line just as reliably as a failed dosing unit. This is why we treat FFS film as a process component that has to be engineered. Off-the-shelf material does not work here.

Four industries, four completely different films

From the outside an FFS bag looks the same in every industry. From the inside these are four different engineering problems.

01 · Chemicals and petrochemicals

The largest user of FFS technology

Polymer granulates (PE, PP, PVC), fertilizers, road salt, household chemicals. Here the decisive factors are seal integrity and moisture barrier: fertilizer that picks up water cakes together and comes back as a complaint.

Risk · Some chemical products react with the film itself. More on this below, as it is one of the most interesting failure mechanisms.

02 · Agriculture, agri-inputs, animal feed

Bags that stand in the sun

Feed for livestock and pets, seed, grain, garden soil, peat, bark mulch. The bags often stand outdoors for an entire season. Without UV stabilization the film goes brittle within a few months. For growing media and bark mulch a micro-perforation pattern is used so the bag breathes without taking in water.

Risk · Every micro-perforation is a potential crack initiator. What matters is the geometry and distribution of the perforation, not its mere presence.

03 · Construction

Where paper loses

Cement, mortars, renders, sand, decorative aggregates, abrasive materials. FFS bags are replacing paper wherever the product has to be fully protected from the weather.

Risk · De-aeration of powdered product during filling, and abrasion from sharp-edged aggregate. Cement on a building site does not forgive weak film.

04 · Food industry

Mechanics plus compliance

Sugar, salt, flour, milk powder, bakery ingredients. On top of the mechanical requirements come food contact compliance and often an oxygen barrier.

Risk · Film without documented compliance with Regulations 1935/2004 and 10/2011 is not even in the running.

The conclusion: the question “how much does FFS film cost” is the wrong question. The right one is: what exactly are you packing, how long does it sit, and under what conditions.

Why bags split after three weeks rather than straight away

Back to the scene at the start, because this is the most common and most misleading complaint scenario in FFS. When the split happens tells you more than the split itself:

Splits during filling

A simple diagnosis: the seal is too weak or the film too thin. Visible immediately, on the line, on the first pallet.

Splits after weeks in storage

Entirely different mechanics: the failure develops over time, under constant load. Three mechanisms account for the majority of these cases.

Mechanism 01

Environmental stress cracking (ESC)

Surfactants from fertilizers, detergents from household chemicals and oils from certain animal feeds act on polyethylene like a silent attacker. Film under constant stress from the weight of the stack, combined with contact with such a substance, produces micro-cracks that grow over weeks.

From the outside nothing is visible. Until suddenly everything is.

Mechanism 02

Creep under stack load

The bottom bags on a pallet stacked several layers high are under constant pressure for the whole storage period. Film with insufficient creep resistance slowly flows and splits at the corners and along the seals, where stresses concentrate.

The failure starts at the bottom of the pallet.

Mechanism 03

Static electricity and dust in the seal

Electrostatically charged tubular film pulls product particles into the cross-seal area. That seal passes inspection on the line but contains micro-channels which open up after weeks under stack load. The remedy is often an ionizing bar with dust extraction ahead of the sealing station rather than a change of film.

A mechanism almost nobody considers.

Before we recommend a change of film, we ask for the split bags and examine a cross-section of the seal. The location of the split tells you what failed. Thicker film does not fix a wrong diagnosis.

Flexo printing: the same bag sells and protects

In retail the FFS bag takes on a second function: it is consumer packaging. Pet food, garden soil and decorative aggregates compete in the outdoor yard of a building supply yard exactly as products compete on a shelf, through graphics.

Flexographic printing in up to 10 colors turns the bag into a brand carrier with no compromise on the mechanical properties of the film. The condition: ink and varnish have to withstand what the film withstands, meaning abrasion in transport, moisture and sunlight in outdoor storage. Print that fades after a month in the yard reduces the perceived value of the product before anyone checks what is inside the bag.

TechnologyFlexo, up to 10 colors

SubstrateTubular / semi-tubular / flat film

ResistanceAbrasion, moisture, UV exposure

SpecificationPrint and film as one document

This is why we treat print design as part of the same technical specification as film gauge and formulation. One specification, one supplier, one line of responsibility.

What you actually get working with Kablonex

We are writing this as a manufacturer, so let us be explicit about what stands behind our recommendations.

production lines

25,000t/year

production capacity

colors in flexo printing

site: extrusion, printing, converting

We extrude, print and convert the film at a single site. One company is accountable for the tubing, the print and the way the bag behaves on your line, with no blame shifting between a film supplier and a printing house.

On top of that come our own regranulation operation POD ECO and the Closed Loop program. Production waste returns to the cycle, and for customers who need recycled content in their packaging we can calculate and document it rather than simply declare it. Under PPWR requirements this stops being a reputational topic and becomes a condition of entry to tenders.

Quality at system level: ISO 9001, BRC Packaging Materials, EcoVadis rating. For food applications: films with documented food contact compliance.

And one thing that cannot be written into a certificate: before we send a quotation, we ask questions about your application. What are you packing, how heavy is the portion, how many layers on the pallet, outdoor storage or indoor, which FFS machine, what cycle rate. If a film supplier does not ask these questions, they are quoting you goods rather than a component of your process.

Reality check: 5 questions before your next film order

Did your film specification come out of an analysis of the application, or was it copied from an order placed years ago?
Do you know how many pallet layers your bags withstand in long-term storage, and who calculated it?
Do bags kept outdoors have confirmed UV stabilization for the real exposure period?
At the last complaint, did anyone examine a cross-section of the seal before proposing thicker film?
Does your print withstand the same conditions as the film it is printed on?

Problem

You answer “I don’t know” to two or more of the questions above, and the bags split only in storage, when the cost of a complaint is at its highest.

Solution

Send us a bag or a description of the application through the form below this article: product, weight, machine, storage conditions. You can also attach the technical specification.

Result

You receive a diagnosis and a specification for film and print engineered for your process, not a quotation from a price list. We reply the same working day.

Author

Radosław Koperski

Head of Research and Development · R&D Manager

At Kablonex he is responsible for film formulations and structures engineered for specific applications, product development across the NEX lines, and material compliance with PPWR and food contact requirements.

He takes complaints apart in this order: location of the split, cross-section of the seal, process parameters on the customer’s line, and only last the film formulation. The problem is usually found earlier than the end of that list.

Technical questions: ask@kablonex.com.pl · Contact