Barrier Properties in Flexible Packaging: What Buyers Need to Understand

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:

• oxygen
• moisture
• light
• aroma
• grease or oils

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:

• oxidation
• moisture gain
• moisture loss
• flavor changes
• aroma loss
• clumping
• texture changes
• color degradation

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.

What Are Barrier Properties in Flexible Packaging?

Barrier properties describe how effectively a packaging material resists the movement of substances or energy through the package.

The most common include:

• oxygen barrier
• moisture barrier
• light barrier
• aroma barrier
• grease resistance

Flexible packaging structures are often engineered using multiple layers because one polymer rarely performs every job equally well.

For example:

• one layer may provide printability
• another may provide oxygen barrier
• another may provide moisture resistance
• another may provide the heat-seal surface

Barrier performance therefore needs to be evaluated at the structure level, not simply by asking what one material is made from.

Why Barrier Requirements Differ by Product

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:

1. Identify the product's likely failure mode.
2. Determine what environmental exposure contributes to that failure.
3. Select packaging with appropriate barrier properties.
4. Validate the finished package.

Starting with the product prevents both under-specifying and over-engineering the packaging.

Oxygen Barrier

Oxygen can contribute to chemical changes in many packaged products.

Potential effects include:

• oxidation
• rancidity
• flavor degradation
• aroma changes
• color changes
• degradation of oxygen-sensitive ingredients

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?.

Products That May Need Oxygen Barrier

Examples can include:

• coffee
• nuts
• snack foods
• oils
• certain supplements
• probiotics
• products containing oxidation-sensitive ingredients

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 Barrier

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:

• powders
• crackers
• snacks
• pet treats
• supplements
• gummies

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.

Moisture Gain

Products that absorb environmental moisture may experience:

• clumping
• caking
• loss of crispness
• texture changes
• sticking
• reduced flowability

Hydration powders and powdered supplements are common examples where moisture control may be important.

Moisture Loss

Some products deteriorate when water leaves the package.

Possible effects include:

• drying
• hardening
• reduced chew quality
• texture degradation

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 Barrier

Light can trigger changes in certain products and ingredients.

Potential effects include:

• color fading
• oxidation
• flavor changes
• degradation of photosensitive compounds

Packaging can reduce light exposure using structures such as:

• foil
• metallized films
• opaque pigments
• printed coverage

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 Barrier

Aroma can move both into and out of a package.

Aroma loss can affect products such as:

• coffee
• spices
• flavored powders
• snacks
• botanical products

Packaging may also need to limit external odors from reaching the product.

This becomes particularly important when:

• products are stored near strongly scented goods
• multiple SKUs share warehouse space
• aroma is central to consumer perception

Aroma-barrier performance often correlates with strong gas-barrier structures, but the actual material system still needs to be evaluated.

Grease and Oil Resistance

Some products can challenge packaging through direct contact with:

• fats
• oils
• grease

The package may need to prevent:

• staining
• weakening
• delamination
• migration through the structure

Examples can include:

• snacks
• pet foods
• oily ingredients

Grease resistance is a different requirement from oxygen or moisture barrier and should be considered separately.

Flexible Packaging Usually Uses Multiple Layers

Many flexible packages use laminated or coextruded structures.

A simplified laminate might include:

Outer Layer

Often selected for:

• printing
• stiffness
• durability

Barrier Layer

Provides specialized protection against:

• oxygen
• moisture
• light
• aroma

Sealant Layer

Provides:

• product-contact surface
• heat sealing
• package closure

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 and Barrier Performance

PET is commonly used in flexible packaging because it can provide:

• good strength
• dimensional stability
• heat resistance
• strong print performance

Clear PET alone is not typically selected as an extreme oxygen- or moisture-barrier material.

It is often combined with other layers such as:

• metallized PET
• foil
• EVOH-based structures
• sealant films

Its role may therefore be primarily mechanical and printable rather than barrier-driven.

Polyethylene and Moisture Barrier

PE is widely used as:

• a sealant layer
• a moisture-resistant layer
• part of mono-material structures

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 and Oxygen Barrier

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

Metallized films use a very thin metal layer deposited onto a polymer substrate.

They can provide significant improvements in:

• oxygen barrier
• moisture barrier
• aroma protection
• light blocking

Metallized structures are commonly used in applications such as:

• snacks
• coffee
• supplements
• powders

Their actual barrier performance depends on the entire construction and the quality of the metallization.

Aluminum Foil

Aluminum foil can provide extremely strong protection against:

• oxygen
• moisture
• light
• aroma transmission

That makes foil useful for demanding applications.

But foil also introduces considerations such as:

• stiffness
• flex-crack potential
• cost
• recycling complexity

It should be used when the product requirement justifies it rather than automatically treated as the default premium solution.

Nylon

Nylon, or polyamide, is often used when packages need additional:

• puncture resistance
• toughness
• mechanical durability

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.

Coatings Can Add Barrier

Barrier can also be created or improved using coatings.

Examples may include:

• oxide coatings
• specialty polymer coatings
• vapor-deposited layers

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.

Barrier Film Is Not the Same as Barrier Packaging

A film can test extremely well in the laboratory.

The finished package may still fail if it contains:

• weak seals
• channels
• pinholes
• flex cracks
• poor closures
• damaged gussets

The package must therefore be treated as a complete system.

This is one of the most important principles in flexible packaging.

Seals Are Part of the Barrier

Once film is converted into a package, seals become potential pathways for environmental exposure.

Seal performance can be affected by:

• temperature
• dwell time
• pressure
• contamination
• sealant selection
• line speed

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.

Closures Affect the Package System

Features such as:

• zippers
• spouts
• valves

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.

Package Size Matters

Barrier transmission is related to exposed material area.

That means the same film can perform differently when used in:

• a small sachet
• a medium pouch
• a large bulk bag

because the total surface area changes.

Package geometry also affects:

• seal length
• headspace
• product-to-package ratio

Finished-package calculations are therefore more useful than relying only on film-level numbers.

Headspace Matters

Oxygen already inside the package at sealing can affect product stability.

Sources include:

• ambient air
• trapped air in powder
• package headspace
• filling conditions

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:

• nitrogen flushing
• vacuum
• modified atmosphere

Those process decisions work alongside barrier film rather than replacing it.

Barrier Performance Changes With Environment

Film does not experience the same conditions throughout a product's life.

Packaging may encounter:

• high humidity
• high temperatures
• cold storage
• freight trailers
• retail shelves

Temperature and humidity can affect transmission behavior.

This is one reason product storage and distribution conditions should be part of barrier-film selection.

OTR and WVTR Need Test Conditions

If you are comparing supplier data, ask:

• What test method was used?
• At what temperature?
• At what relative humidity?
• What film gauge was tested?
• Was the result measured on raw film or the full laminate?

A number without this information may not be meaningfully comparable to another supplier's result.

Do Not Use Generic Barrier Targets

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:

• formulation
• acceptable change
• package dimensions
• initial product condition
• storage environment
• desired shelf life

Generic targets can result in either:

• inadequate protection
• unnecessary material and cost

The product should drive the target.

Higher Barrier Is Not Always Better

Barrier performance often comes with tradeoffs.

Increasing barrier may affect:

• cost
• flexibility
• clarity
• recyclability
• machine performance

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.

Barrier and Recyclability

Traditional high-barrier laminates often combine several different materials.

That can complicate recycling.

Newer structures may use:

• PE-family materials
• PP-family materials
• EVOH
• barrier coatings

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.

Mono-Material Does Not Mean One Layer

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:

• different PE grades
• tie layers
• thin barrier components

depending on the design.

For a deeper look at material construction, see our flexible packaging materials guide.

Lamination vs Coextrusion

Multiple layers can be combined in different ways.

Lamination

Separate films are manufactured and then bonded together.

This allows different substrates to be combined for:

• printability
• barrier
• sealing
• strength

Coextrusion

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:

• materials
• barrier requirement
• printing
• economics
• application

Our guide to Laminated vs Coextruded Flexible Film explores that comparison in more detail.

Printing and Barrier

Printing usually occurs on or near the outer part of the structure.

Depending on the design, graphics may be:

• surface printed
• reverse printed and trapped inside the laminate

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.

Barrier Testing

Common barrier measurements include:

• OTR
• WVTR
• light transmission

But those measurements answer specific questions.

They do not replace:

• seal testing
• package-integrity testing
• stability testing

A complete qualification program may use all of them.

Shelf-Life Validation Is a Separate Step

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:

• finished-package testing
• line trials
• accelerated stability
• real-time stability
• change control

This article focuses on understanding the barrier properties themselves.

Choosing Barrier by Product Risk

A practical starting framework is:

Moisture-Sensitive Product

Prioritize:

• WVTR
• seal integrity
• moisture-resistant layers

Oxygen-Sensitive Product

Prioritize:

• OTR
• initial headspace oxygen
• gas-barrier layers

Light-Sensitive Product

Prioritize:

• opacity
• light transmission

Aroma-Sensitive Product

Prioritize:

• volatile-compound retention
• strong gas-barrier structures

Puncture-Prone Product

Add:

• mechanical strength
• nylon or other toughness layers where appropriate

The final structure may need to solve several of these simultaneously.

Questions to Ask Your Packaging Supplier

Ask:

Product

• What is the product sensitive to?
• What shelf life is expected?
• What distribution conditions are anticipated?

Material

• What is the complete structure?
• What does each layer do?
• What are the OTR and WVTR values?
• What are the test conditions?

Finished Package

• How will seals affect performance?
• Are zippers, valves, or spouts involved?
• Has the finished package been tested?

Production

• Is the structure compatible with the filling equipment?
• Has it been run on similar machinery?
• What sealant and operating range are recommended?

These questions are more useful than simply requesting “high-barrier film.”

Barrier Properties in Flexible Packaging: The Short Answer

Flexible-packaging barrier properties control exposure to:

• oxygen
• moisture
• light
• aroma
• oils and grease

Different materials contribute different functions.

Common examples include:

• PE for sealing and moisture resistance
• PET for strength and printability
• EVOH for oxygen barrier
• metallized films for gas and light barrier
• foil for demanding barrier requirements
• nylon for toughness

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.

Need Help Selecting a Barrier Structure?

Western Packaging can help evaluate flexible packaging based on:

• product type
• sensitivity to oxygen or moisture
• target shelf life
• package format
• filling equipment
• expected volume

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.