When someone hands you a flexible packaging specification, two numbers tend to show up quickly:
OTR and WVTR.
Both describe how well a packaging material slows something from passing through it. But they measure two completely different threats to the product.
And depending on what you're packaging, one may matter significantly more than the other.
The mistake is assuming that a film described as "high barrier" automatically provides the protection your product actually needs.
It may not.
OTR stands for Oxygen Transmission Rate.
It measures the rate at which oxygen passes through a packaging material under specified test conditions.
In general:
Lower OTR = greater resistance to oxygen transmission.
That matters for products that can be damaged by oxidation.
Examples include:
Oxygen entering a package can contribute to rancidity, flavor changes, color degradation, and changes in certain sensitive ingredients.
That makes OTR an important part of the specification for many food and nutraceutical applications.
But it isn't the whole specification.
WVTR stands for Water Vapor Transmission Rate.
It measures the rate at which water vapor passes through a packaging material under specified conditions.
In general:
Lower WVTR = greater resistance to moisture transmission.
That becomes particularly important for products that absorb moisture from the environment or need to retain a specific moisture level.
Examples include:
Moisture entering the package can cause powders to clump, reduce flowability, soften crispy products, alter texture, or otherwise change how the product performs.
For those applications, a film can have excellent oxygen protection and still fail because its moisture barrier isn't sufficient.
This is the most important distinction.
A material that performs well against oxygen does not necessarily perform equally well against water vapor.
And the reverse is also true.
Think of them as two separate specifications:
| Measurement | What It Measures | Common Product Risk |
|---|---|---|
| OTR | Oxygen passing through the material | Oxidation, rancidity, flavor or ingredient degradation |
| WVTR | Water vapor passing through the material | Clumping, moisture pickup, texture change, loss of crispness |
That means the correct question isn't:
"Is this a high-barrier film?"
It's:
"High barrier against what?"
OTR and WVTR values shouldn't be compared without looking at the test conditions.
Temperature and humidity affect transmission behavior, and the reported result only makes sense when you know the conditions under which the material was tested.
For example, two film suppliers may provide different OTR values for what appears to be a similar structure.
If those measurements were taken under different temperature or humidity conditions, comparing the numbers directly can be misleading.
When evaluating specifications, look for:
ASTM D3985 is one standardized method used to measure oxygen transmission through plastic films and laminates.
ASTM F1249 is commonly used for measuring water vapor transmission through flexible barrier materials.
The important point for a packaging buyer isn't memorizing the test methods.
It's making sure you're comparing equivalent data.
For many dry powders, WVTR can be the first problem to solve.
A moisture-sensitive powder may:
Products such as hydration powders, protein powders, collagen, greens, powdered supplements, and certain food ingredients can all be affected.
But oxygen may still matter.
If the formula includes oxygen-sensitive ingredients, flavors, oils, vitamins, or other actives, then OTR also becomes part of the specification.
So a powder package may need excellent moisture protection and meaningful oxygen protection.
That's why the product formulation has to drive the structure.
Coffee is heavily affected by oxygen.
Once roasted, exposure to oxygen contributes to staling and loss of desirable flavor and aroma.
That makes low OTR important.
But coffee packaging also has to address:
So even here, choosing packaging based on one number alone misses much of the system.
The barrier structure, pouch construction, seals, and valve all have to work together.
For a crunchy snack, moisture can be the obvious enemy.
If enough water vapor enters the package, texture suffers.
But products containing fats or oils can also oxidize, making OTR relevant to flavor stability and rancidity.
That is why snack structures often balance:
Again, there isn't one universal "snack film."
Gummies are especially interesting because moisture movement can occur in either direction.
Depending on the formulation and storage environment, the product can gain or lose moisture.
That can affect:
Some formulations or active ingredients may also require oxygen or light protection.
The correct structure depends on the actual product—not simply the fact that it is a gummy.
A low OTR or WVTR does not automatically guarantee a particular shelf life.
Film performance is only part of the finished package.
Actual product protection also depends on factors such as:
A technically excellent film can still produce a poor package if the seals aren't reliable.
Likewise, an unnecessarily aggressive barrier structure may add cost without materially improving the finished product.
The objective is not to chase the lowest possible number.
The objective is to determine the barrier performance the application actually needs.
OTR and WVTR are typically achieved through a combination of layers rather than one material doing everything.
A flexible structure might include:
Provides:
Provides some combination of:
Provides:
Materials such as PET, PE, nylon, EVOH, metallized films, foil, and coatings can all play different roles.
The structure has to work as a system.
A good barrier film still has to print, form, fill, seal, ship, and open correctly.
It's tempting to assume that more protection is always safer.
Commercially, that's not always the right answer.
Increasing barrier can mean:
If a less complex structure achieves the required product performance, moving to a substantially higher barrier may only add unnecessary cost.
That's why good specification work starts with the required outcome.
Instead of starting with a film, start with the application.
Determine what actually causes degradation.
Is it sensitive to:
A package intended to protect a product for six months may require a different structure than one expected to remain stable for 18 or 24 months.
A package sitting in climate-controlled storage faces a different environment than one exposed to heat and humidity through distribution.
Rollstock, stand-up pouches, sachets, stick packs, and other formats create different package geometries and sealing requirements.
The structure still has to run.
That includes:
Once the risks are understood, OTR and WVTR targets can become part of the package specification.
Where shelf life is critical, evaluate the finished package and the actual product rather than relying solely on the raw-film specification.
If you're comparing structures, ask for more than a material name.
Request:
And give your supplier enough information to make a useful recommendation.
At minimum, provide:
If oxygen damages your product, OTR matters.
If moisture damages your product, WVTR matters.
If both can damage it, both matter.
And in many real packaging applications, the answer is exactly that: both numbers matter, but not necessarily equally.
The job is to determine which threat is driving the package requirement and build the film structure around that application.
You don't need to know the exact OTR, WVTR, or laminate structure before starting a packaging conversation.
Tell us:
Western Packaging can help work backward from those requirements to an appropriate flexible packaging structure.
Learn more about barrier films for flexible packaging, or talk with our team about your application.