In flexible packaging selection, "barriers" often determine shelf life and product experience. However, higher barrier values are not always better. The key factors are product sensitivities, target shelf life, storage and transportation environment, and the sealing window of the production line. This article uses the OTR/WVTR approach to break down flexible packaging barrier selection into actionable steps, helping you make decisions based on the "lowest achievable barrier" to avoid over-configuration or under-selection.

I. What Exactly Does Barrier Block? 

The essence of barrier selection in flexible packaging is to control the exchange rate between the external environment and the contents. Common impacts mainly come from three categories:

Oxygen: Causes oil oxidation, flavor degradation, and color darkening, especially noticeable in nuts/coffee/snacks.

Moisture: Leads to softening, clumping, and decreased crispness; powders/seasonings also easily absorb moisture.

Aroma and Volatile Matter: "Aroma dissipates" or external odors enter the packaging, affecting taste and quality consistency.

If you want to clarify the system first, you can read this article on the site: What is Flexible Packaging?, then returning to this article for structural selection will be smoother.

II. OTR and WVTR: How to Use Them During Selection

OTR (Oxygen Transmission Rate) measures the rate at which oxygen permeates through the material; WVTR (Water Vapor Transmission Rate) measures the rate at which water vapor permeates through. When it comes to selection, it's recommended to follow this path:

First, set your goals: Target shelf life (e.g., 6/9/12 months) + actual storage and transportation conditions (temperature and humidity, whether it's a high-temperature season, whether it involves long-distance transportation).

Next, identify sensitivity points: For oxygen-sensitive products, prioritize OTR; for moisture-sensitive products, prioritize WVTR; for aroma-sensitive products, consider overall barrier properties + sealing system.

Finally, conduct validation: Small-batch sampling + key tests (sealing performance/sealing strength/transportation simulation), and evaluate OTR/WVTR indicators if necessary.

III. How to Structure: Layer Roles and Combination Logic

From a structural logic perspective, flexible packaging typically consists of three collaborative parts: "printing support + barrier core + heat sealing implementation":

Outer Layer: Responsible for print performance, abrasion and scratch resistance, a certain degree of stiffness, and aesthetic texture.

Barrier Layer: Determines the upper limit of OTR/WVTR, crucial for shelf life.

Heat Sealing Layer: Determines the sealing window and sealing reliability, also determining production line stability.

For foods with high "freshness" requirements, besides the material itself, the sealing system (heat sealing parameters, sealing shape, zipper/tear-off opening, etc.) has a significant impact on the result.

IV. Practical Selection Process: Making Decisions Based on "Lowest Achievable Barrier"

It is recommended to follow one main principle: choose the lowest barrier solution that can consistently meet standards, allocating the budget to areas that truly affect the outcome.

Identify Sensitive Points: Sensitive to oxygen / Sensitive to moisture / Sensitive to aroma / Sensitive to light.

Confirm Form and Process: Stand-up pouches/roll films/spout pouches, etc. Filling temperature and speed affect the choice of heat-seal layer.

Define Acceptance Items: Sealing performance, seal strength, transportation simulation (drop/compression/puncture resistance), and conduct barrier index assessment if necessary.

Validate before mass production: Avoid situations where "theoretically strong structure, but unstable seal in mass production."

V. Common Misconceptions (Many projects get stuck here)

Misconception 1: Maximizing barrier protection. Increases costs, but may not significantly improve real-world shelf performance.

Misconception 2: Ignoring the sealing window. A mismatch between the heat-seal layer and temperature/speed can easily lead to air leakage or a brittle seal.

Misconception 3: Judging only by samples, ignoring the environment. Humid storage, transportation compression, and high temperatures during peak seasons can all alter the results.

VI. Quick Self-Checklist (Use this to align your factory)

Product Type and Sensitive Factors (Oxygen/Moisture/Aroma/Light)
Target Shelf Life and Actual Storage and Transportation Environment (Temperature, Humidity/Transportation Mileage)
Packaging Form and Functional Components (Zipper/Easy-Tear Opening/Vent Valve, etc.)
Production Line Process (Filling Temperature, Speed, Sealing Method)
Acceptance Test Items (Sealing Performance/Sealing Strength/Transportation Simulation/OTR/WVTR if necessary)