Flexible packaging does more than contain a product.
One of its most important jobs is controlling what can move through the package.
Depending on the product, that may mean limiting:
These are commonly referred to as barrier properties.
The right barrier helps protect product quality through storage and distribution. The wrong barrier can lead to problems such as:
The goal is not always to create the strongest possible barrier.
It is to understand which environmental exposures matter to the product and how much protection the package needs.
For a broader look at commercial film options built around those requirements, see our barrier films guide.
Barrier properties describe how effectively a packaging material resists the movement of substances or energy through the package.
The most common include:
Flexible packaging structures are often engineered using multiple layers because one polymer rarely performs every job equally well.
For example:
Barrier performance therefore needs to be evaluated at the structure level, not simply by asking what one material is made from.
Not every product is vulnerable to the same environmental conditions.
A dry powder might be primarily sensitive to moisture.
Roasted coffee may be highly sensitive to oxygen and aroma loss.
A gummy may need moisture control in both directions.
A light-sensitive ingredient may require opacity regardless of its oxygen-barrier requirement.
That means the correct sequence is:
Starting with the product prevents both under-specifying and over-engineering the packaging.
Oxygen can contribute to chemical changes in many packaged products.
Potential effects include:
A package's resistance to oxygen transmission is commonly described using OTR — oxygen transmission rate.
In general:
Lower OTR means less oxygen passes through the material under the specified test conditions.
But OTR should never be considered without its test conditions.
Temperature and humidity can affect the result.
For a deeper explanation, see OTR vs WVTR: Which Matters for Your Packaging?.
Examples can include:
The actual OTR requirement should come from product sensitivity and shelf-life objectives rather than a generic category target.
Two products in the same category may legitimately require different packaging.
Moisture movement can occur in either direction.
Some products need protection from moisture entering the package.
Others need protection from moisture leaving it.
Examples of moisture-sensitive products include:
Moisture transmission is commonly measured using WVTR — water vapor transmission rate.
In general:
Lower WVTR means stronger resistance to water-vapor transmission under the specified test conditions.
Again, the test conditions matter.
Products that absorb environmental moisture may experience:
Hydration powders and powdered supplements are common examples where moisture control may be important.
Some products deteriorate when water leaves the package.
Possible effects include:
Certain gummies and soft foods can fall into this category.
Barrier is therefore not simply about keeping moisture out.
It is about maintaining the product's desired internal environment.
Light can trigger changes in certain products and ingredients.
Potential effects include:
Packaging can reduce light exposure using structures such as:
A clear package offers merchandising advantages but may not be appropriate when strong light protection is required.
That tradeoff should be resolved during package development rather than after artwork is finalized.
Aroma can move both into and out of a package.
Aroma loss can affect products such as:
Packaging may also need to limit external odors from reaching the product.
This becomes particularly important when:
Aroma-barrier performance often correlates with strong gas-barrier structures, but the actual material system still needs to be evaluated.
Some products can challenge packaging through direct contact with:
The package may need to prevent:
Examples can include:
Grease resistance is a different requirement from oxygen or moisture barrier and should be considered separately.
Many flexible packages use laminated or coextruded structures.
A simplified laminate might include:
Often selected for:
Provides specialized protection against:
Provides:
The combination creates the finished package properties.
For an overview of PET, PE, BOPP, CPP, EVOH, foil, metallized films, nylon, and related substrates, see our flexible packaging materials guide.
PET is commonly used in flexible packaging because it can provide:
Clear PET alone is not typically selected as an extreme oxygen- or moisture-barrier material.
It is often combined with other layers such as:
Its role may therefore be primarily mechanical and printable rather than barrier-driven.
PE is widely used as:
It can provide useful moisture resistance and strong sealing characteristics.
Its oxygen-barrier performance is generally more limited than materials specifically designed for oxygen control.
That is why PE often appears in a multilayer structure alongside another barrier technology.
EVOH is known for strong oxygen-barrier performance.
It is frequently incorporated inside multilayer films.
One important characteristic is that its oxygen-barrier performance is affected by humidity.
For this reason, EVOH is usually protected by other layers that help shield it from moisture.
This is a good example of why the complete film structure matters more than the name of one resin.
Metallized films use a very thin metal layer deposited onto a polymer substrate.
They can provide significant improvements in:
Metallized structures are commonly used in applications such as:
Their actual barrier performance depends on the entire construction and the quality of the metallization.
Aluminum foil can provide extremely strong protection against:
That makes foil useful for demanding applications.
But foil also introduces considerations such as:
It should be used when the product requirement justifies it rather than automatically treated as the default premium solution.
Nylon, or polyamide, is often used when packages need additional:
Some nylon materials also contribute useful gas-barrier properties.
However, nylon can absorb moisture, which can influence its properties.
Its role in a structure is often mechanical as much as barrier-related.
Barrier can also be created or improved using coatings.
Examples may include:
These technologies can allow clear structures to reach higher barrier levels without relying on opaque metallization or foil.
Again, the finished structure and actual tested performance should guide selection.
A film can test extremely well in the laboratory.
The finished package may still fail if it contains:
The package must therefore be treated as a complete system.
This is one of the most important principles in flexible packaging.
Once film is converted into a package, seals become potential pathways for environmental exposure.
Seal performance can be affected by:
Powder products are especially challenging because fine particles can enter the seal area.
A high-barrier laminate with poor seals is still a poor barrier package.
Features such as:
change the package.
For example, a coffee degassing valve serves an important function but also becomes another component in the package's overall barrier system.
Likewise, a zipper improves reclosure convenience after opening but does not recreate the original unopened package environment.
Barrier should be evaluated with all functional components included.
Barrier transmission is related to exposed material area.
That means the same film can perform differently when used in:
because the total surface area changes.
Package geometry also affects:
Finished-package calculations are therefore more useful than relying only on film-level numbers.
Oxygen already inside the package at sealing can affect product stability.
Sources include:
A low-OTR film limits future oxygen entering the package.
It does not remove oxygen already present.
For highly oxygen-sensitive applications, packaging operations may also consider:
Those process decisions work alongside barrier film rather than replacing it.
Film does not experience the same conditions throughout a product's life.
Packaging may encounter:
Temperature and humidity can affect transmission behavior.
This is one reason product storage and distribution conditions should be part of barrier-film selection.
If you are comparing supplier data, ask:
A number without this information may not be meaningfully comparable to another supplier's result.
It is tempting to say:
Every powder needs X WVTR.
or:
Every coffee bag needs Y OTR.
That is rarely a strong specification strategy.
Barrier requirements depend on:
Generic targets can result in either:
The product should drive the target.
Barrier performance often comes with tradeoffs.
Increasing barrier may affect:
If a lower-cost structure already meets the product requirement, moving to an extreme barrier may not provide additional commercial value.
A well-designed package is right-sized, not simply maximized.
Traditional high-barrier laminates often combine several different materials.
That can complicate recycling.
Newer structures may use:
to improve compatibility with certain recycling pathways.
But recyclability should be evaluated carefully.
A package that is theoretically more recyclable but fails to protect the product can increase product waste.
Barrier performance and end-of-life design need to be considered together.
The term mono-material can be confusing.
A mono-material structure may still contain several layers.
The goal is usually to keep those layers primarily within one compatible polymer family.
For example, a PE-family structure may include:
depending on the design.
For a deeper look at material construction, see our flexible packaging materials guide.
Multiple layers can be combined in different ways.
Separate films are manufactured and then bonded together.
This allows different substrates to be combined for:
Multiple molten polymer layers are produced together as one film structure.
This can create efficient multilayer structures without a separate lamination step.
Neither approach is universally better.
The decision depends on:
Our guide to Laminated vs Coextruded Flexible Film explores that comparison in more detail.
Printing usually occurs on or near the outer part of the structure.
Depending on the design, graphics may be:
The printing process should be compatible with the film and lamination system.
The package should also be evaluated after converting because manufacturing can affect the final structure.
Common barrier measurements include:
But those measurements answer specific questions.
They do not replace:
A complete qualification program may use all of them.
Barrier measurements can help identify candidate structures.
They do not prove a particular shelf life by themselves.
If you need to establish whether the finished package actually supports a supplement's target shelf life, see How to Validate Barrier Packaging for Supplement Shelf Life.
That article covers:
This article focuses on understanding the barrier properties themselves.
A practical starting framework is:
Prioritize:
Prioritize:
Prioritize:
Prioritize:
Add:
The final structure may need to solve several of these simultaneously.
Ask:
These questions are more useful than simply requesting “high-barrier film.”
Flexible-packaging barrier properties control exposure to:
Different materials contribute different functions.
Common examples include:
But the film structure alone does not determine package performance.
The final result depends on:
material + seals + closures + package geometry + filling process + storage conditions.
The right barrier is the one proven to meet the actual product requirement.
Western Packaging can help evaluate flexible packaging based on:
From there, we can compare structures without over- or under-specifying the application.
Explore our barrier films, flexible packaging materials, and custom flexible packaging resources to continue the project.