Is PP Better than PET Moisture Barrier?

The Moisture Barrier Question

For packaging professionals selecting strapping or film materials, moisture barrier performance can be a critical consideration. Products stored in humid environments, shipped across climate zones, or packed with moisture-sensitive goods require packaging that keeps moisture out. This raises a common question: is PP strap better than PET as a moisture barrier? When comparing water vapor transmission rates, data shows that oriented polypropylene (OPP) film offers approximately 5.4 times better moisture barrier performance than PET of equivalent thickness. Understanding these material differences helps procurement professionals select the right packaging materials for their specific applications.

At Jushuo Packaging, we frequently receive this question from buyers evaluating PP strap for applications where moisture exposure is a concern. Our production data confirms that PP strap’s inherent moisture resistance—a result of its non-polar molecular structure—makes it suitable for outdoor storage, agricultural, and humid-environment applications.

1. Moisture Barrier: The Data

1.1 Barrier Performance Comparison

Published test data provides a clear answer to the moisture barrier question. According to independent testing comparing PET and oriented polypropylene (OPP) films of the same thickness, BOPP demonstrated significantly superior water vapor barrier performance :

The data shows BOPP’s water vapor transmission rate is approximately 5.4 times lower than PET’s, demonstrating clearly superior moisture barrier performance. Industry sources confirm that oriented polypropylene's moisture barrier is approximately 3 times better than PET’s . The difference in water vapor barrier properties is attributed to differences in polymer molecular polarity .

1.2 Why PP Has Better Moisture Barrier

The superior moisture barrier of PP compared to PET relates to polymer chemistry. PP is a non-polar hydrocarbon polymer with low affinity for water molecules, resulting in lower moisture permeability. PET contains ester groups that have higher polarity, creating more interaction sites for water molecules to pass through the polymer structure .

According to packaging science literature, the water vapor barrier performance of polyolefins like PP is inherently superior to that of polyesters like PET due to their hydrophobic nature and lower free volume for water molecule diffusion.

2. The Complete Barrier Picture

2.1 Oxygen Barrier: PET’s Strength

While PP excels as a moisture barrier, PET offers a different advantage: superior oxygen barrier. The same test data shows PET’s oxygen transmission rate is approximately 23 times lower than BOPP’s . This makes PET the preferred choice for applications where oxygen ingress is the primary concern—such as food packaging requiring extended shelf life.

2.2 Barrier Summary

This inverse relationship between moisture and oxygen barrier is a well-known phenomenon in polymer packaging science—different materials excel at different types of barrier protection.

3. Implications for PP Strap Selection

3.1 When Moisture Barrier Matters for Strapping

For most PP strap applications, moisture barrier is not the primary selection criterion. Strapping is typically used to secure loads rather than provide protective packaging. However, in certain scenarios, moisture resistance becomes relevant:

• Outdoor storage: PP strap’s inherent moisture resistance helps maintain performance in humid or wet conditions

• Cold chain applications: Moisture from condensation can affect strap tension and integrity

• Agricultural packaging: Hay, cotton, and other agricultural products are often stored outdoors

Jushuo Packaging's PP strap offers inherent moisture resistance as part of its material properties, making it suitable for these demanding applications.

3.2 Material Selection Guidance

For packaging professionals selecting strapping materials:

Summary

Is PP better than PET as a moisture barrier? Data confirms: yes, PP provides superior moisture barrier performance. BOPP film’s water vapor transmission rate is approximately 5.4 times lower than PET’s, making PP the clear winner for applications requiring moisture protection. However, the barrier picture is more nuanced: PET excels as an oxygen barrier, with performance approximately 23 times better than PP.

For strapping applications, moisture barrier is typically not the primary selection criterion, but PP’s inherent moisture resistance—a result of its non-polar hydrocarbon structure—makes it suitable for outdoor storage, agricultural, and humid-environment applications. When selecting between PP and PET strap, consider the complete application requirements: moisture exposure, load weight, and whether oxygen barrier is also a consideration.

Jushuo Packaging offers comprehensive PP strap solutions with inherent moisture resistance for demanding applications. Our 5 PP production lines with 20,000 tons annual capacity ensure consistent quality across all specifications. We support clients through material selection based on application requirements, including moisture exposure assessment.

If you need assistance selecting the right strapping material for your moisture-sensitive application, please send an email to sales@jushuopackaging.com, and our professional team will provide one-on-one support.

References

1. SpecialChem. “The Opportunities in Oriented Polypropylene (OPP) – Material Properties Comparison.” SpecialChem.com, 2025.

2. Toray Industries. “Biaxially Oriented Polypropylene Film – Technical Data Sheet.” Toray.com, 2024.

3. ASTM International. “ASTM F1249 – Standard Test Method for Water Vapor Transmission Rate Through Plastic Film.” ASTM.org, 2020.

4. European Committee for Standardization. “EN 13394:2001 – Packaging – Strapping – Specifications for Polypropylene Strapping.” CEN.eu, 2001.

5. International Organization for Standardization. “ISO 9001:2015 – Quality Management Systems – Requirements.” ISO.org, 2015.