How to Make PP (Polypropylene) Thermoformed Sheets: A Comprehensive Guide

John Li
May 13, 2025
4:57 am

Polypropylene (PP) thermoformed sheets are a versatile and cost-effective solution for industries ranging from packaging to automotive. But how are these sheets made, and what makes them so special? In this blog post, we’ll dive into the process of creating PP thermoformed sheets¹, exploring everything from the basics to technical details, and provide practical tools to help you make informed decisions.

Table of Contents Hide

1. What are PP Thermoformed Sheets?
2. What are the Common Types of PP Used in Thermoforming?
3. What are the Steps in the PP Thermoforming Process?
4. What are the Key Design Considerations for PP Thermoformed Sheets?
5. What are the Applications of PP Thermoformed Sheets?
6. How Does PP Thermoforming Compare to Other Processes?
7. What are the Challenges in PP Thermoforming?
8. Conclusion

What are PP Thermoformed Sheets?

PP thermoformed sheets are created by heating polypropylene² sheets to a pliable state and shaping them using molds. This process is widely adopted due to its efficiency and PP’s unique properties, such as being lightweight and chemically resistant.

Polypropylene (PP) is a thermoplastic polymer known for its low density, high chemical resistance, and good mechanical properties. Thermoforming involves heating a plastic sheet to a pliable state (165-180°C for PP), stretching it over a mold using vacuum, pressure, or mechanical force, and cooling it to retain the shape.

A machine processing green and orange sheets — PP Thermoformed Sheets

Understanding this process and its applications is key to unlocking the benefits of PP thermoformed sheets in your industry. Read on to discover how different PP grades and design choices influence the final product.

PP thermoformed sheets are only used in packaging applications.False

While common in packaging, PP thermoformed sheets also find applications in medical, automotive, and consumer goods industries due to their versatility.

What are the Common Types of PP Used in Thermoforming?

Different grades of PP are utilized in thermoforming, each with distinct properties tailored to specific applications.

Rolls of BOPP film being manufactured in a factory setting — PP Thermoformed Sheets

Common PP types for thermoforming include homopolymer PP³ for stiffness, impact copolymer PP⁴ for durability, and random copolymer PP⁵ for flexibility, used in packaging, medical, and automotive industries.

Material Type	Characteristics	Applications
Homopolymer PP	High stiffness, good heat resistance	Hot fill, microwave applications
Impact Copolymer PP	Enhanced impact resistance, lower clarity	Freezer-microwave use
Random Copolymer PP	Flexible, good for refrigerated applications	Refrigerated packaging
Filled PP	Improved stiffness with fillers (e.g., talc, calcium carbonate)	Structural parts
Multi-layer PP	Barrier properties for oxygen/moisture, used in packaging	Oxygen-sensitive packaging

Homopolymer PP

Homopolymer PP offers high stiffness and heat resistance, making it perfect for hot fill and microwave-safe packaging. However, its brittleness requires careful handling during thermoforming.

Impact Copolymer PP

Impact copolymer PP provides enhanced impact resistance, ideal for durable products like freezer-to-microwave containers. Its lower clarity limits its use in applications needing transparency.

Random Copolymer PP

Random copolymer PP is flexible and excels in refrigerated environments, making it a top choice for food packaging. Its flexibility also aids in forming deeper draws.

All PP grades are equally suitable for thermoforming.False

Different PP grades have varying properties that affect their suitability for specific applications and forming conditions.

What are the Steps in the PP Thermoforming Process?

The creation of PP thermoformed sheets involves two primary stages: sheet production and thermoforming. Precision at each step ensures a high-quality final product.

The PP thermoforming process⁶ includes extruding PP sheets, heating them to 165-180°C, forming them over a mold using vacuum or pressure, and cooling to set the shape, used in packaging, medical, and automotive industries.

An image of industrial machinery with rollers and yellow components — PP Thermoformed Sheets

Sheet Production

Raw Material Preparation: PP resin⁷ is pre-crystallized to enhance processing stability.
Extrusion: Resin is melted and compressed in an extruder.
Filtration and Pumping: Molten PP is filtered to remove impurities.
Co-extrusion (if applicable): Used for multi-layer sheets like PP-EVOH-PP.
Die Forming: Material is evenly shaped in the die head.
Cooling and Shaping: Sheets are cooled via three-roll sheeting.
Cutting: Waste edges are trimmed to size.
Final Cooling: Sheets are naturally cooled and conveyed.

Thermoforming

Heating: PP sheets are heated to 165-180°C.
Forming: Softened sheets are stretched over a mold using vacuum, pressure, or mechanical force.
Cooling: Formed sheets are cooled to solidify the shape.
Trimming and Finishing: Excess material is removed, and secondary operations like printing are applied.

The thermoforming process always results in uniform thickness.False

PP’s low melt strength can cause sagging and uneven thickness, especially in deep draws.

What are the Key Design Considerations for PP Thermoformed Sheets?

Designing for PP thermoformed sheets requires specific guidelines to ensure functionality and manufacturability.

A large industrial machine with rotating metal rollers used for processing materials — PP Thermoformed Sheets

Key design considerations include draft angles⁸ (3-4° for male molds), limiting draw ratio⁹s to 1:1, avoiding undercuts, and accounting for PP’s shrinkage and warpage.

Design Aspect	Recommendation
Draft Angles	3-4° for male molds, 1.5-2° for female molds
Draw Ratio	Limit to 1:1 for standard processes
Undercuts	Avoid; small undercuts¹⁰ possible with thin parts or moveable molds
Tolerances	Forming: +/- 0.030” up to 12”; Trim-trim: +/- 0.015” up to 12”
Shrinkage and Warpage	Increase crystallinity, use small spherulites
Secondary Operations	Use special adhesives, riveting, ultrasonic welding, or painting

Draft Angles

Draft angles facilitate part removal from molds. For PP, use 3-4° for male molds and 1.5-2° for female molds, with larger angles for deep draws or textured surfaces.

A machine producing clear plastic wrap with large rolls of plastic material — PP Thermoformed Sheets

Draw Ratio

Limit the draw ratio (depth-to-width) to 1:1 for standard processes to avoid thinning or part failure.

Undercuts

Avoid undercuts to simplify molding. Small undercuts are possible with thin parts or moveable mold sections.

PP thermoformed sheets can be designed with complex undercuts without issues.False

Undercuts complicate the molding process and should be avoided or minimized in design.

What are the Applications of PP Thermoformed Sheets?

PP thermoformed sheets shine across industries due to their versatility, affordability, and eco-friendly attributes.

PP thermoformed sheets are used in packaging, medical, automotive, and consumer goods for their lightweight, chemical resistance¹¹, and recyclability¹².

Black handling tray for transport and storage — vacuum forming products

Packaging

Ideal for food trays, blister packs, and containers, PP offers moisture barriers and food-safe properties, extending to cosmetics and electronics packaging.

Medical Industry

Used for sterile packaging and medical trays, PP ensures hygiene and chemical resistance for items like surgical instrument trays.

Automotive

Lightweight and durable, PP is perfect for interior components like dashboards, enhancing fuel efficiency.

Open Duraliner cargo box with a black textured surface — vacuum forming products

Consumer Goods

From cases to display stands and stationery, PP’s flexibility and cost-effectiveness make it a popular choice.

PP thermoformed sheets are unsuitable for high-temperature applications.False

Homopolymer PP, with its high heat resistance, is suitable for hot fill and microwave applications.

How Does PP Thermoforming Compare to Other Processes?

PP thermoforming has unique strengths and limitations when compared to alternative plastic forming methods.

PP thermoforming is cost-effective for large parts¹³ and offers recyclability, but it’s less suitable for complex geometries¹⁴ compared to injection molding or blow molding.

Workers operating a machine that processes large sheets of blue material in an industrial facility — PP Thermoformed Sheets

Comparison with Injection Molding

Cost: Lower tooling costs make thermoforming economical for large parts.
Complexity: Injection molding excels in complex, precise geometries.

Comparison with Blow Molding

Detail: Thermoforming provides better detail for flat or shallow parts¹⁵.
Hollow Structures: Blow molding suits hollow items like bottles.

Vacuum Forming vs. Pressure Forming

Vacuum Forming: Simple and cost-effective for shallow parts.
Pressure Forming: Offers sharper edges for detailed applications.

PP thermoforming is the only process for creating plastic sheets.False

There are various processes for creating plastic sheets, including injection molding, blow molding, and rotational molding, each with its own advantages.

What are the Challenges in PP Thermoforming?

Despite its advantages, PP thermoforming presents challenges that require careful management.

Challenges in PP thermoforming include managing PP’s low melt strength, which can cause sagging, and its uneven shrinkage, which may lead to warpage.

Several large rolls of shiny metal foil — PP Thermoformed Sheets

Low Melt Strength

PP’s low melt strength can lead to sagging during heating, causing uneven thickness, especially in deep draws.

Uneven Shrinkage

PP’s uneven shrinkage can result in warpage. Mitigate this by increasing crystallinity and using small spherulites.

Limited Clarity

Standard PP grades lack clarity, though clarified PP can be used for transparent needs like cosmetic packaging.

PP thermoforming always results in clear, transparent parts.False

Standard PP grades have limited clarity; clarified PP is needed for transparent applications.

Conclusion

Making PP thermoformed sheets involves a meticulous process of sheet production and thermoforming, with attention to material grades and design guidelines. By mastering this process, its applications, and related technologies, manufacturers can harness PP’s strengths for cost-effective, recyclable, and versatile products.

Explore the advantages of PP thermoformed sheets and how they can enhance efficiency and cost-effectiveness in your industry. ↩
Discover the unique properties of polypropylene and its diverse applications, which can inform your material choices in production. ↩
Explore the advantages of homopolymer PP for packaging applications, including its stiffness and heat resistance. ↩
Learn how impact copolymer PP improves durability in products, making it ideal for various applications. ↩
Discover why random copolymer PP is preferred for refrigerated packaging due to its flexibility and performance. ↩
Explore this link to understand the detailed steps and applications of the PP thermoforming process in various industries. ↩
Learn about PP resin's properties and its crucial role in manufacturing high-quality thermoformed products. ↩
Understanding draft angles is crucial for successful mold design and part removal, ensuring efficiency in production. ↩
Exploring draw ratio impacts can help optimize designs and prevent part failures during manufacturing. ↩
Learning about undercuts can guide you in making informed design choices that enhance manufacturability. ↩
Learn about the importance of chemical resistance in medical applications, ensuring safety and reliability in healthcare products. ↩
Discover the significance of recyclability in packaging, promoting sustainability and environmental responsibility in product design. ↩
Explore this link to understand how cost-effective methods can optimize production for large plastic components. ↩
Discover why injection molding is preferred for intricate designs and how it can enhance product quality. ↩
Learn how thermoforming achieves superior detail in specific applications, making it a valuable technique in manufacturing. ↩