Soft chews — whether they are pet treats, functional gummies-style confections, or semi-moist snacks — fail differently from dry goods. The product still holds water, and that water stays active inside the pack for the whole shelf life. It moves, it softens textures that were supposed to stay firm, it feeds mould if the formulation allows, and it complicates every seal on the line. A structure that performs beautifully on a dry biscuit can be the wrong answer here.

This guide takes a specification-first view of soft chew packaging: define what the product actually does to the pack, write those behaviours into measurable requirements, and then verify them before committing to production volumes.

Water activity, not just water content

The first specification to fix is water activity (aw), which is not the same as moisture content. Two soft chews with identical moisture percentages can behave differently if one binds its water and one leaves it free. Free water drives microbial risk, texture change and moisture migration into drier components.

The brand’s product team, not the converter, owns this number. What the packaging brief needs from them is:

• the target water-activity range and its production tolerance;
• whether the recipe relies on humectants, acids or preservatives — because those change how the product responds to any moisture that enters or leaves;
• the texture endpoints that define “acceptable” at end of shelf life.

Without those three inputs, any barrier discussion is guesswork dressed up as engineering.

Where the moisture actually travels

Soft chew packs usually fail from internal moisture movement rather than outside ingress. Common routes:

• Product to headspace, headspace to cold spots. Water evaporates from the chew, condenses on the cooler film surface, and drips back — concentrating wet patches that mark the pack and localise spoilage risk.
• Wet product to dry insert or desiccant. A moisture absorber can pull water from the product itself if the dosing is wrong, hardening the chew instead of protecting it.
• Component to component. In mixed packs (a soft chew next to a dry biscuit), moisture migrates until the two sides converge — often ruining both.

Each route demands a different countermeasure, and none of them is solved by adding barrier alone. Head-space control, piece separation, and pack geometry belong in the same conversation.

Barrier and structure candidates worth screening

With the moisture behaviour defined, structure screening becomes a normal exercise in matching materials to duties. Typical candidate directions for soft chews include:

• PET / adhesive / EVOH / PE laminates, where oxygen control matters alongside moisture — the EVOH barrier resin guide explains when the layer earns its cost and where humidity sensitivity complicates it;
• nylon (PA)-containing structures when the product has edges or the pack faces abrasion — see the nylon film guide for the puncture-versus-moisture trade-off;
• metallized or foil structures where the moisture and aroma duties are severe, accepting the loss of product visibility;
• all-PE mono-material builds where recyclability targets dominate and the barrier duty is moderate.

The screening rule is simple: every quoted transmission value must come with its test method and conditions, and every candidate must be validated on the actual chew. Soft chews make this non-negotiable because their own moisture participates in the outcome.

Seals that open on purpose

Soft chews create two conflicting seal demands. The factory seal must hold through distribution, yet the consumer must open the pack without crushing the product, and many formats need reclosing afterwards.

• Peelable sealants give a controlled opening force. Specify the force window, not just “peelable” — too weak splits the pouch, too strong tears the film elsewhere.
• Tear notches work when the chew tolerates the opening path; they fail when the notch redirects through a wet, weak zone of the film.
• Resealable features suit multi-serve packs but add a wide seal zone that competes with product space on small sachets.

Seal-strength verification on finished packs matters more here than on dry goods, because fat and water at the seal area change real-world results. Heat-seal strength testing references such as ASTM F88/F88M and water-vapor transmission references such as ASTM E96/E96M give buyers a common language for stating what was measured and how.

Verification before scale-up

A soft chew programme earns its reliability in the verification stage. A workable sequence:

1. Fix the specification. Water activity, texture endpoints, fat, aroma, piece geometry — in writing, with tolerances.
2. Map the supply chain. Temperature and humidity range by leg: filling, warehouse, retail, consumer pantry.
3. Screen structures on data, then shortlist two or three candidates.
4. Run filling trials at production speed, capturing seal contamination events and jaw settings.
5. Test finished packs: seal strength, leak method appropriate to the risk, drop and compression where the channel demands it.
6. Hold real storage trials with the actual formulation, tracking the texture and microbiological checkpoints the product team defined.

Where a pet soft chew is the subject, the regulatory frame adds its own checkpoints; FEDIAF in Europe and AAFCO in the United States publish the labelling and composition context that the pack’s claims must respect.

FAQ

Is a metallized film always the right choice for soft chews?

No. Metallized layers offer strong moisture and light barrier, but the product’s own water activity, the need for visibility, and sealant behaviour all influence the decision. Screen metallized against clear high-barrier and foil candidates on the real product.

Why did my chew harden even though the barrier looked excellent?

The pack may be pulling moisture out as well as keeping moisture out. Over-dosed absorbers, excess headspace exchange, or a formulation with free water can dry the product. Check the product-side specification before blaming the film.

What should a first trial report contain?

At minimum: the structure and its documented test conditions, jaw settings and dwell, seal contamination observations, finished-pack seal and leak results against pre-agreed criteria, and the storage trial plan with its checkpoints.

For contrast, the dry side of the category is covered in the guide to dry pet food packaging, and adjacent soft-texture problems — stickiness, moisture movement and reseal behaviour — appear in the gummy packaging guide and the dried fruit packaging solutions overview.