Why does rPET behave differently from virgin PET in thermoforming?

Recycled PET has become one of the most discussed materials in plastic packaging production, and for good reason. As sustainability regulations tighten across Europe and globally, more manufacturers are shifting toward rPET to meet both legislative requirements and consumer expectations. But anyone who has run rPET through a thermoform machine knows it does not behave like virgin PET. The differences are real, they affect every stage of the process, and understanding them is the first step toward consistent, high-quality output.

This post breaks down exactly why rPET presents unique challenges in thermoform packaging production, from material composition through to machine demands and output quality, and how to approach each one practically.

How rPET’s material composition affects processing

The fundamental difference between rPET and virgin PET starts at the molecular level. Virgin PET is produced to a precise, consistent specification. rPET, by contrast, is a blend of post-consumer and post-industrial recycled material, which means its intrinsic viscosity, moisture content, and contamination levels can vary from batch to batch depending on the source stream and the recycling process used.

This variability directly affects how the material flows and stretches during thermoform molding. Lower intrinsic viscosity, which is common in heavily recycled material, results in reduced melt strength. This makes the sheet more prone to thinning unevenly during forming, particularly in deep-draw applications. Residual moisture is another critical factor: rPET that has not been dried adequately will hydrolytically degrade during heating, causing visible defects such as bubbles, haze, or brittleness in the finished part. Predrying rPET to the correct moisture level, typically below 50 ppm, is not optional. It is a prerequisite for stable thermoform plastic production.

Temperature and pressure settings for rPET

Getting the temperature profile right for rPET requires more attention than with virgin material, and it often requires more frequent adjustment. Because rPET’s thermal properties shift with its recycled content and contamination profile, the processing window tends to be narrower. Running too cool leads to incomplete forming and stress whitening; running too hot risks degradation, discoloration, and loss of mechanical properties in the finished thermoformed cups or trays.

Heating zones need to be calibrated carefully to achieve uniform sheet temperature across the full web width. Infrared heating systems with zone-by-zone control are particularly valuable here, as they allow fine-tuned compensation for any inconsistency in the rPET sheet. On the pressure side, forming pressures may need to be slightly increased compared to virgin PET to achieve full definition in complex geometries, especially in areas with tight radii or detailed surface features. The key is to test and document settings for each rPET grade and supplier, treating each source as a distinct material rather than assuming interchangeability.

Tooling and machine demands when running rPET

Running rPET puts greater demands on both tooling and the thermoforming machine itself. The material’s variability means that tooling designed for virgin PET may not perform identically with recycled material. Forming tools need to be robust enough to handle the slightly different flow characteristics, and venting must be adequate to prevent trapped air from causing surface defects.

On the machine side, stability and precision become even more important. Any flex or misalignment in the forming station is amplified when working with a material that has a narrower processing window. Machines with a rigid, well-supported forming station, precise parallelism between upper and lower tool halves, and consistent clamping force deliver far more reliable results with rPET than machines where mechanical tolerances are looser. Servo-driven systems that allow precise control over motion profiles also help, since the ability to fine-tune the speed and force of the forming stroke gives operators more flexibility to compensate for batch-to-batch material variation.

Maintenance intervals may also need to be reviewed when switching to rPET. Recycled material can carry trace contaminants that accelerate wear on certain machine components, so keeping a close eye on wear patterns and adjusting service schedules accordingly is a sound practice.

Quality and output challenges in rPET production

Consistent part quality is the central challenge in industrial thermoform production with rPET. The material’s variability introduces a higher risk of defects, including wall thickness inconsistency, surface haze, colour variation, and reduced impact strength compared to virgin PET equivalents. Each of these can translate directly into increased reject rates and higher cost per unit produced.

Wall thickness distribution deserves particular attention. Because rPET can have lower melt strength, material tends to thin more aggressively in areas of high stretch. For deep-draw parts such as yogurt cups or portion pots, this can lead to bases or sidewalls that fall below the minimum thickness specification. Optimising the pre-stretch plug geometry and plug advance timing is often the most effective lever for improving thickness distribution without changing the material itself.

Colour consistency is another practical concern. Post-consumer rPET frequently carries a slight yellow or grey tint that varies between batches. For packaging applications where aesthetics matter, this can require either careful supplier selection, blending strategies, or the use of food-grade colour masterbatch to achieve an acceptable result.

Balancing sustainability targets with production efficiency

The push toward rPET is not going away. Regulatory frameworks such as the EU Packaging and Packaging Waste Regulation are driving minimum recycled content requirements, and brand owners are setting their own sustainability commitments that flow directly into specification requirements for packaging suppliers. The question for production teams is not whether to run rPET, but how to do it efficiently.

The good news is that with the right process setup, rPET production can be highly competitive. The additional process discipline required, tighter material handling, more careful temperature management, and regular tooling checks pay dividends in consistent output and lower scrap rates. Energy consumption is also a factor worth considering: optimising heating efficiency and cycle times not only reduces costs but also improves the overall environmental footprint of the operation, which reinforces the sustainability case for using recycled content in the first place.

Looking ahead to 2026 and beyond, the availability and quality of food-grade rPET are improving as collection and recycling infrastructure matures. This means the material consistency challenges described above will gradually reduce, making rPET an increasingly practical choice for high-volume thermoform packaging production. Manufacturers who invest now in process knowledge and machine capability for rPET will be well positioned as recycled content mandates increase.

How GABLER Thermoform helps with rPET thermoforming

We understand that switching to or scaling up rPET production is not just a material decision. It is a machine and process decision. Our high-end thermoforming machines are engineered with the precision and stability that rPET demands, and our technology is designed to handle the variability that comes with recycled materials without compromising output quality or cycle rates.

Rigid forming stations built from cast steel ensure the parallelism and clamping consistency that rPET’s narrower processing window requires
Separate servo drives for lifting and swiveling motion give operators precise control over forming profiles, making it easier to compensate for batch-to-batch material variation
Innovative crankshaft technology optimises motion sequences and reduces tool wear, which matters more when running materials with trace contamination
Industry 4.0 readiness with state-of-the-art sensor technology and remote access enables real-time process monitoring to catch quality deviations early
Processing capability for rPET and biodegradable PLA foil, supporting manufacturers as sustainable material requirements evolve

Whether running a compact stand-alone machine or a large-scale complete line with extrusion, we offer the full package from installation through to spare parts supply, so production teams can focus on output rather than troubleshooting. Explore our full machine range or get in touch with us directly to discuss how your rPET production goals can be met with the right thermoforming technology.