Buyers Guide to PET and PP Films: Key Specs for Packaging

Why PET and PP Films Dominate Flexible Packaging

PET and PP films form the backbone of most flexible packaging structures. PET, or polyethylene terephthalate, provides high oxygen barrier and good heat resistance. PP, or polypropylene, offers excellent moisture resistance and easy processing.

Buyers often select between these two based on the product being packaged. Oxygen-sensitive items like coffee, nuts, and fresh produce often favor PET. Moisture-sensitive products like chips, snacks, and dry goods often favor PP. Laminates frequently combine both to balance barrier and processability.

Barrier Properties: Oxygen, Moisture, and Water Vapor

Barrier performance is the first specification to evaluate. PET has a low oxygen transmission rate and performs well for oxygen-sensitive contents. Its oxygen barrier remains stable across a broad temperature range.

PP has a high water vapor barrier but a relatively high oxygen transmission rate. This makes PP suitable for moisture control but less ideal for long shelf life oxygen-sensitive products.

When specifying barrier films, consider the target shelf life and storage conditions. A product stored at higher temperatures or in humid environments will demand different barrier characteristics than a product kept cool and dry.

Mechanical Properties: Tensile Strength and Stretch

Mechanical performance affects how the film behaves during processing and in service. PET has high tensile strength and good dimensional stability. It resists stretching and maintains shape under tension.

PP is more flexible and has good elongation. It stretches without breaking and handles creasing well. This makes PP suitable for pouches that require folding or gussets.

Buyers should specify tensile strength, elongation at break, and tear resistance. These values help confirm that the film will withstand forming, filling, and sealing without failure.

Heat Resistance and Sealing Behavior

PET can handle higher temperatures than PP. Its heat resistance makes it suitable for retort packaging and products that undergo thermal processing. PET also seals at higher temperatures, which gives more flexibility in sealing line setup.

PP seals at lower temperatures and has good seal strength. It is widely used in pouches and bags that go through standard vertical form-fill-seal lines. However, PP has a lower heat deflection point and may soften at higher temperatures.

The sealing temperature of the film must match the sealing equipment. If the film seals too low, it may not form a reliable seal. If it seals too high, it may degrade or cause defects. Confirm the recommended sealing temperature range with the supplier.

Material Selection Criteria Table

The table below summarizes the key criteria for comparing PET and PP films. Use it as a starting point for discussions with suppliers and internal engineering teams.

Criterion	What to look for	Why it matters
Barrier properties	Oxygen transmission rate, water vapor transmission rate	Determines shelf life and product freshness
Heat resistance	Heat deflection temperature, maximum processing temperature	Affects suitability for retort or hot-fill applications
Mechanical strength	Tensile strength, elongation, tear resistance	Ensures film survives forming and handling
Sealing behavior	Sealing temperature range, seal strength	Matches equipment and prevents seal failures
Clarity	Transmittance, haze	Affects visual appeal and product visibility
Cost and lead time	Price per square meter, delivery windows	Supports budget planning and inventory control

Downstream Processing Compatibility

Film selection is not only about the film itself. It must work with the rest of the packaging structure. PET and PP have different surface energies, which affect adhesion to other layers in a laminate.

PET generally has higher surface energy than PP. This makes it easier to laminate with certain adhesives and barrier materials. PP often requires corona treatment or other surface activation to achieve good adhesion.

When specifying a laminate, confirm that the adhesive or coextruded layer is compatible with both PET and PP. A mismatch can cause delamination during processing or after filling.

Also consider the forming method. Stretch film, blow film, or cast film each have different surface treatments and mechanical behaviors. The film type must match the forming process to avoid defects like wrinkles, pinholes, or weak seals.

Practical Specification Checks Before Ordering

Before placing an order, confirm the following details with the supplier:

1. Film thickness in microns and the acceptable tolerance range.
2. Film width and whether the roll is slitted or on a core.
3. Surface treatment, such as corona or plasma, if adhesion is required.
4. Barrier performance values, including oxygen and water vapor transmission rates.
5. Sealing temperature range and recommended seal width.
6. Roll direction, since some films perform differently across versus across the roll.
7. Packaging and handling instructions for long-distance transport.

These checks reduce the risk of receiving film that does not perform as expected. They also create a clear reference for quality disputes.

Common Mistakes in PET and PP Film Selection

Buyers often focus on price alone and skip technical verification. This can lead to film that passes initial tests but fails in service.

Another common mistake is assuming a single film type will work for all products in a portfolio. A PET film that performs well for coffee may not be suitable for a product that requires high moisture barrier. Conversely, a PP film that works for chips may not provide enough oxygen barrier for nuts.

A third mistake is ignoring roll handling. A film that is easy to process on one line may be difficult on another due to differences in stiffness, stretch, or core size. Confirm how the film will be loaded and unwound.

Decision Checklist for Choosing PET or PP Film

Use this checklist when evaluating a new film specification or switching suppliers.

• Does the film meet the required oxygen and water vapor barrier values for the target shelf life?
• Does the film withstand the maximum processing temperature of the packaging line?
• Does the film seal reliably with the current equipment and settings?
• Is the film compatible with the other layers in the laminate structure?
• Does the film thickness and width match the forming process?
• Are the supplier’s lead times and minimum order quantities acceptable?
• Have you tested the film in your actual packaging environment, not just in a lab?

If the answer to any of these questions is no, re-evaluate the specification before ordering.

Balancing Performance and Cost

Performance and cost are always in tension. A higher barrier film may extend shelf life but increase cost. A thinner film may reduce material usage but increase the risk of defects.

The goal is not to buy the cheapest film. It is to buy the film that performs reliably for the intended application. A small increase in film performance can prevent costly recalls, waste, and customer complaints.

Work with suppliers to find the right balance. Ask for trade-off options, such as different thicknesses or surface treatments, that meet the same performance target at a lower cost.

Final Thoughts on PET and PP Film Selection

PET and PP films are workhorses in flexible packaging. Each has strengths and limitations. PET excels in oxygen barrier and heat resistance. PP excels in moisture barrier and processability.

The right choice depends on the product, the packaging structure, and the processing line. A clear specification, backed by testing and supplier verification, will lead to a reliable packaging solution.