I’ve always been fascinated by how plastic materials behave under heat. Whether I’m working with low-density polyethylene (LDPE), high-density polyethylene (HDPE), or polyvinyl chloride (PVC), one thing remains constant — knowing the plastic melting temperature is crucial to achieving the best results.
In this post, I’ll walk you through what I’ve learned about the melting point of plastics, how mold temperature affects injection molding, and why understanding these temperature ranges matters in both manufacturing and recycling.
What Is the Melting Point of Plastics?
The melting point of a plastic is the temperature at which it changes from a solid state to a liquid. The higher the melting point, the more resistant the plastic is to heat and other environmental factors. Different types of plastics have different melting points; some can withstand temperatures up to 300°F (148°C), while others may melt at much lower temperatures.
The melting point of a plastic is the temperature where the plastic transitions from a high-elastic (solid) to a viscous flowable state. In simple terms, this is the melting temperature range at which a plastic material melts enough to be reshaped or molded. Different plastic polymers have different melting temperature ranges depending on their molecular structure and polymer chain length. Crystalline plastics, for instance, have a well-defined melting point, while amorphous plastics gradually soften across a glass transition temperature rather than melting sharply.
As a general rule, the higher the melting temperature, the greater the material’s heat resistance and dimensional stability — both essential for maintaining structural integrity under high temperature applications.
The Four Key Temperatures for Plastics
Glass Transition Temperature – the temperature at which an amorphous polymer changes from a hard/glassy state to a soft/leathery or rubber state
Melting Temperature – the temperature at which a plastic material softens and begins to flow under heat
Flow Temperature – A higher-temperature state for amorphous plastics, where they become a viscous fluid. This temperature is significantly higher than the glass transition temperature
Decomposition Temperature – The temperature at which the plastic material begins to break down chemically.
The Role of Mold Temperature in Injection Molding, and Injection Blow Molding (IBM)
From my experience in injection molding and injection blow molding, I’ve learned that controlled mold temperature plays a critical role in the product quality. The temperature of the mold cavity when molten plastic is injected determines how the plastic flows and sets.
Any deviation can cause surface defects, while proper mold temperature ensures better part performance and production efficiency.
Incorrect injection molding temperatures can lead to visible defects or weakened mechanical properties. Meanwhile, maintaining the correct mold temperatures helps improve manufacturing efficiency and, surface finish, and mechanical strength.
What is Mold temperature of Plastics?
Mold temperature of plastics is the temperature at which plastic is injected into a mold to form desired products. The mold temperature of plastic affects both the quality and performance of a molded product. Different types of plastics have different optimal mold temperatures, so it’s important to know what kind of plastic is being used before beginning a project.
Common Types of Plastic with Their Melting Points and Mold Temperature
| Materials | Melt Temperature | Mold Temperature |
| ABS | 190-270℃ | 50-90℃ |
| ABS/PC | 245-265℃ | 70-110℃ |
| Acetal | 180-210℃ | 80–100℃ |
| Acrylic | 220-250℃ | 79-107℃ |
| HDPE | 210-270℃ | 30-70℃ |
| LDPE | 180-240 ℃ | 50-70℃ |
| Nylon 6 | 230-290℃ | 70-120℃ |
| Nylon 6 (30% GF) | 250-290℃ | 70-120℃ |
| Nylon 6/6 | 270-300℃ | 70-120℃ |
| Nylon 6/6 (33% GF) | 280-300℃ | 60-130℃ |
| Nylon 11 | 220-250℃ | 70-120℃ |
| NYLON 12 | 190-200℃ | 70-120℃ |
| PEEK | 350-390℃ | 120-160℃ |
| PC | 280-320℃ | 85-120℃ |
| PBT | 240-275℃ | 60-90℃ |
| PET | 260-280℃ | 20-30℃ |
| PEI | 340–360℃ | 20-30℃ |
| PPA | 325℃ | 60-130℃ |
| Polypropylene Copolymer | 200-280℃ | 20-30℃ |
| PP (30% TALC-FILLED) | 240-290℃ | 30-50℃ |
| PP (30% GF) | 250-290℃ | 40-80℃ |
| PS | 170-280℃ | 30-60℃ |
| PS (30% GF) | 250-290℃ | 40-80℃ |
| PVC | 170-190℃ | 20-40℃ |
| TPE | 260-320℃ | 40-70℃ |
Tips on How to Safely Melt Plastic
Safety is a critical factor when experimenting with plastic melting. Over the years, I’ve followed a few non-negotiable practices:
1. Ensure proper ventilation to prevent inhaling toxic fumes.
2. Use gloves and protective eyewear when handling melted plastics.
3. Start at the lower end of the melting temperature range and increase gradually.
4. Avoid exceeding the decomposition temperature to maintain the mechanical strength of the material.
5. Allow melted plastic to cool naturally before touching or reshaping.
Importance of Recycling
In my own projects, I’ve seen how plastic recycling can drastically reduce production costs and material waste. Recycled plastics, when melted correctly, often retain their mechanical properties and chemical resistance, allowing them to be repurposed for automotive components, consumer goods, and even high temperature applications.
Recycling also supports sustainability — minimizing pollution, conserving energy, and promoting a circular economy in manufacturing.
Conclusion
Understanding the melting point of plastics and managing mold temperature are essential skills in both injection molding and recycling.
By mastering temperature characteristics and melting behavior, I’ve been able to improve my production process, ensure dimensional stability, and extend the life of my final products.
Whether you’re a manufacturer or an enthusiast exploring plastic melting and recycling, remember: precise temperature control and material knowledge are your best tools for achieving efficiency, safety, and sustainability.