Polyester (PET) Films: Built to Perform When the Heat Is On

As temperatures rise, both seasonally and within increasingly demanding supply chains, the performance of packaging materials is under greater scrutiny than ever. Reliability, consistency, and protection are no longer “nice to have” qualities; they’re essential.

One material that continues to play a critical role in high-performance flexible packaging is Polyester (PET) film.

Can PET Be Heat Sealable? Absolutely.

One common misconception is that polyester film cannot be heat sealed. While standard PET itself is not inherently heat sealable, it can easily be engineered to deliver excellent sealing performance.

This is typically achieved through:

• Coextrusion with sealant layers (such as polyethylene)
• Application of heat seal coatings
• Lamination into multi-layer structures

These enhancements transform PET into a highly effective heat sealable solution, combining its natural strength with reliable seal integrity.

What Are Heat Sealable Films?

Heat sealable films are engineered materials designed to bond to themselves or another surface when heat and pressure are applied.

This seal forms:

• A closed pack to protect the product
• A barrier against contamination
• Often a tamper-evident closure

The key lies not just in the film itself, but in the sealant layer or coating that activates under heat.

Why Heat Sealing Matters More Than Ever

In today’s packaging environment, films must perform under increasingly demanding conditions:

• Elevated ambient temperatures during heatwaves
• High-speed packing lines requiring consistent sealing windows
• Complex global distribution with fluctuating conditions

A failure in seal integrity can lead to:

Product spoilage
Leakage or contamination
Waste and brand damage

That’s why reliable heat seal performance is non-negotiable.

The Structure Behind the Seal

Heat sealable films are rarely single-material. Instead, they are typically multi-layer structures, designed to combine performance features.

A typical construction includes:

Outer layer (e.g. PET or BOPP)

Provides strength, printability, and heat resistance

Barrier layer (optional)

Improves shelf life by limiting oxygen or moisture ingress

Sealant layer (critical component)

Enables the film to bond when heat is applied
 

Foil-Based Lidding

Used for:

• Portion pots (syrup, sauces, dairy)

Features:

• Aluminium layer for maximum barrier
• Heat seal coating (lacquer) for bonding

Ideal for:

• Long shelf life
• Leak-sensitive products

Polypropylene (PP) Films

Common in:

• Microwaveable packaging
• Hot-fill applications

Provides:

• Good heat resistance
• Compatibility with mono-material recyclable designs

Typically found in:

• Bakery
• Fresh produce

Advantages:

• Lightweight
• Cost-efficient

Performance Under Pressure: Key Considerations

A high-performing heat sealable film must deliver:

Consistent seal strength
Across varying temperatures and line speeds

Seal integrity
Preventing leaks and contamination

Controlled peelability
For consumer convenience where required

Wide sealing window
Allowing flexibility in production conditions

These factors become even more critical during heatwaves, when elevated temperatures can impact material behaviour and sealing consistency.

Real-World Applications

Heat sealable films are used across virtually every packaging sector:

• Chilled and ready meals → PET-based lidding with peelable seals
• Ambient portion pots → foil lids with heat seal lacquer
• Snacks and bakery → flow-wrap films with heat seal layers
• Pet food and healthcare → high-performance laminates

Each application requires a tailored seal solution, matched to both the product and the pack format.

Supporting Efficiency and Sustainability

Modern heat sealable films also support:

• Efficient high-speed production
• Material optimisation (lightweighting)
• Recyclability initiatives through mono-material structures

By selecting the right film design, businesses can balance:

• Performance
• Cost
• Sustainability goals

Final Thoughts: Packaging That Keeps Its Cool

As the industry faces rising temperatures, both literally and operationally, material choice has never been more important.

With the right design and sealing technology, heat sealable PET films offer a powerful combination of durability, consistency, and performance under pressure.

At National Flexible, we work closely with customers to develop packaging solutions that don’t just meet expectations, but perform when it matters most.

💬 Looking to future-proof your packaging against rising temperatures? 

Contact us: marketing@nationalflexible.net | 01274 685566