A small sachet of pet food or pet treats gives a brand many things: a low-commitment trial size, a portion-controlled feeding unit, a colorful billboard at the shelf edge. What it does not give you is tolerance. In a large pouch, a marginal seal is a statistic buried in thousands of units. In a small sachet, the seal is a large share of the total construction, the product is often moist or greasy, and every single unit gets squeezed by a consumer. That is why experienced buyers evaluate pet food sachet packaging in a specific order: seal integrity first, barrier second, cost third, and appearance last among the essentials. This guide walks through the specification, verification and supplier-side questions that ordering should be built around.

Why Small Formats Concentrate Risk at the Seal

Three properties of small sachets push risk toward the seal. First, the seal-to-volume ratio is high, so a larger proportion of every unit is a heat seal. Second, filling is fast and product can easily end up in the seal zone, especially with sticky or oily recipes. Third, the consumer usage pattern is harsh: sachets are torn open with fingers, squeezed to empty, and often carried loose in a pocket or a drawer. A design that looks identical to a competitor’s can behave completely differently depending on how the seal was specified and verified.

This is not an argument for over-engineering. It is an argument for writing the seal requirements down before artwork absorbs all the meeting time.

Write the Seal Specification Before the Artwork

A useful sachet specification answers, in writing, each of the following. If your supplier conversation is not covering these points, the specification is not yet a specification.

Seal Width, Overlap and Geometry

Narrow sachets are usually made as three-side or four-side sealed units, and the back seal geometry interacts with how the sachet handles pressure when squeezed. Wider seals generally tolerate contamination and handling abuse better but consume film and can make tearing open harder. The specification should state the minimum seal width and where the tear notch sits relative to it, so that tear performance and integrity are not quietly traded against each other during a production rush.

Seal Strength and the Peel Question

For a sachet that is torn open, there is a genuine tension between seal strength and openability. You need enough hot tack and final seal strength to survive filling, distribution and squeezing, but the tear path must still run where you want it. The standard way to quantify this is a seal strength test such as ASTM F88, and for finished packages a leak or burst method suited to the format. You do not need to master the test methods; you do need your supplier and your filler to agree on which methods and which acceptance criteria apply, and to record them.

Sealant Layer Selection

The sealant is the layer that actually welds. Sealant choice sets the width of the sealing window on your filling machine: some PE-based sealants are forgiving across a broad temperature range, while higher-barrier or stiffer structures can narrow it. Our backgrounders on polyethylene (PE) in flexible packaging and nylon (PA) film explain how these layers contribute stiffness and puncture resistance when a sachet carries bone fragments, jerky pieces or gritty textures.

Verify Through the Supply Chain, Not Just at the End

Seal integrity is not a certificate you receive with the film roll. It is the combined result of film, machine, product and environment, which means verification has to happen at several points.

Incoming Film Checks

At minimum, verify thickness profile, sealant surface condition and corona treatment level where printing or sealing depends on it. Variations that look trivial on a roll spec sheet, such as gauge bands, show up later as seal windows that move with every new pallet of film.

Pilot Runs on the Actual Machine

Laboratory sealers produce beautiful seams that production jaws cannot reproduce at speed. Any new sachet construction should go through a pilot run on the machine and product it will actually serve, mapping the practical seal window: the range of temperature, pressure and dwell where seals pass your integrity test. If that window is narrow, fix the specification now, because it will narrow further on a humid summer shift.

Distribution Simulation on Filled Sachets

Seals that pass leak testing at the end of the line can still fail in a shipping case. Filled sachets are squeezed by case compression, shaken by vibration and dropped at handoffs. A distribution test profile based on your real logistics chain, run on filled and finished sachets, is the only verification that reflects what the consumer experiences. When a sachet format is new to your brand, budget for this before the first production order, not after the first complaint wave.

What to Ask a Sachet Supplier

Supplier capability in this format shows up in how they answer questions, not in their brochure. A short list that separates experienced converters from resellers:

• Which leak test method do you run on finished sachets, at what frequency, and can you share the records per batch?
• What seal window data do you hold for this structure on machines like ours, and how was it measured?
• How do you document roll-to-roll consistency of the sealant layer?
• What happens when a batch fails: quarantine process, root-cause analysis, and who decides on disposition?

The same diligence applies to moisture and oxygen claims. Barrier values belong to the film structure, but shelf life belongs to the product plus package plus storage condition combination, and only a properly designed study can support the date on the sachet. Regulatory framing differs by market: FEDIAF publishes the European nutritional and labelling framework for pet food, and seal strength for small formats is normally verified to ASTM F88/F88M so that results are comparable between suppliers. Local labelling rules still have to be confirmed against the current regulation for the market in question, while FEDIAF publications describe the European nutritional framework.

Common Seal Failure Modes and What They Point To

When sachets leak in the field, the failure usually falls into one of a few families, and each family points to a different corrective action.

• Product in the seal. Filler dosing, cutoff behavior or fill-level margins need adjustment; the film is rarely the root cause.
• Wrinkled or channel-leaking seals. Film stiffness, gusset behavior and jaw parallelism interact. Look at the machine setup first, then at film thickness uniformity.
• Weak seal with clean surfaces. Seal temperature, dwell or pressure drifted outside the window, or the sealant grade changed. Compare machine logs with the documented window.
• Seal that fails after distribution but not on the line. Flex cracking, seal creep or abrasion during transport. Add distribution testing and review film toughness.

Treating these as diagnostic categories, rather than as one vague “quality problem”, shortens the path between complaint and correction. Buyers who maintain this discipline also find supplier conversations easier, because both sides argue from the same evidence.

Where Appearance Fits

None of this means shelf appearance is unimportant. It means appearance decisions should be made inside a construction that already meets integrity and barrier requirements, not the other way around. Metallic effects, matte surfaces and heavy ink coverage can all interact with seal areas, and a design that keeps ink and coatings away from the seal zones avoids a whole family of defects. For buyers comparing formats, our guides to four-side seal pouch structure and cost and soft chew packaging show how the same logic plays out in adjacent categories, while dry pet food packaging covers where the priorities shift for larger, drier formats.

Frequently Asked Questions

How should a pet food sachet seal specification be written?

Write it as defined values before the artwork is released. That means seal width, overlap, seal geometry, and whether the seal is meant to peel or to hold. Before any pet food sachet packaging structure is approved, a specification that only says “strong seal” cannot be inspected, and two suppliers will read it differently. Add the sealant layer assumed in the structure and the machine settings the specification depends on. This document is the reference for both the incoming-film check and the pilot run, so anything missing from it comes back later as a dispute rather than as a reject. Start from the structure the format needs, as covered in the guide to four-side-seal pouch structure and cost.

Do we need to re-qualify the seal when the film supplier changes?

Yes, even when the declared structure is unchanged. Another supplier can meet the same nominal layers with a different sealant formulation, and the sealing window moves with it. Re-qualifying does not have to mean a new project: an incoming film check plus one pilot run on the real filling machine shows whether the window has shifted. Treating a supplier change as a paperwork update is how a stable product starts leaking once handling is added. Where the sealant choice sits in the structure is explained in the guide to polyethylene sealant layers.

What does it mean when sachets only leak after distribution?

It usually means the seal survived the bench test but not the journey. Vibration, compression and temperature swings open the weakest point of a seal that was already marginal, and small formats concentrate that load on a short seal length. Reproduce it by simulating distribution on filled sachets rather than on flat film, and by checking the same positions on every failed pack. If nothing fails in a proper simulation, the next suspect is seal geometry rather than the film.