Plastic melting point is one of the first properties checked when choosing a material and setting up a process. It decides how a plastic is shaped, how much heat it can handle, and how stable production will be. This guide covers what melting point means, the temperatures of common plastics, the factors that change them, and how melting point affects real manufacturing.
What Is Plastic Melting Point?
Plastic melting point is the temperature at which a solid plastic turns into a flowing liquid. For most plastics, this falls between about 100°C and 350°C, far below the melting point of metals such as aluminum (660°C) or steel (about 1,500°C). The exact value depends on the plastic type and grade.
Plastics that can melt are called thermoplastics. Their melting behavior depends on how the polymer chains are arranged. Based on this structure, thermoplastics are divided into two groups, crystalline and amorphous plastics, and the two groups respond to heat in different ways.
Crystalline vs Amorphous Plastics
Crystalline plastics, such as PP, PE, nylon, POM and PET, contain ordered molecular regions. These regions break down at a fairly high temperature, so a clear melting point can be measured. Once that temperature is passed, the material flows quickly.
Amorphous plastics, such as ABS, PS, PMMA, PVC and PC, have a random molecular structure and no sharp melting point. They soften gradually as temperature rises above the glass transition temperature (Tg), the point where the material changes from rigid to rubbery. Processing then takes place in a higher temperature range where the material flows well enough to be shaped. For these plastics, Tg and the recommended processing range are used in place of a melting point.
How to Measure the Melting Point of Plastic
Differential scanning calorimetry (DSC) is the standard method. A small sample is heated at a controlled rate while heat flow is recorded. Melting appears as a peak, and the glass transition appears as a step change in the curve. Common standards include ASTM D3418 and ISO 11357.
Other methods include melting point apparatus and hot stage microscopy for a quick check of crystalline plastics. For amorphous plastics and heat resistance, Vicat softening temperature (ASTM D1525, ISO 306) and heat deflection temperature (HDT) testing are widely used. For most projects, datasheet values from the material supplier are enough for planning.
Melting Temperatures of Common Plastics
The table below lists typical values for widely used plastics. Exact figures vary with grade, additives, and reinforcement, so the supplier datasheet should always be checked for a specific material.
| Plastic | Structure | Melting Point or Tg | Typical Processing Temperature | Typical Applications |
|---|---|---|---|---|
| ABS | Amorphous | Tg about 105°C | 200 to 250°C | Housings, automotive interior parts |
| PP (Polypropylene) | Crystalline | Tm 160 to 170°C (homopolymer) | 200 to 250°C | Containers, automotive parts, living hinges |
| HDPE | Crystalline | Tm 120 to 135°C | 180 to 250°C | Bottles, pipes, storage containers |
| Nylon 6 (PA6) | Crystalline | Tm about 220°C | 230 to 290°C | Gears, bushings, wear parts |
| Nylon 66 (PA66) | Crystalline | Tm 255 to 265°C | 270 to 300°C | Under-hood parts, connectors, gears |
| PVC | Mostly amorphous | Tg about 80°C | 160 to 200°C | Pipes, cable insulation, profiles |
| Acrylic (PMMA) | Amorphous | Tg about 105°C | 200 to 250°C | Lenses, light covers, display panels |
| PS (Polystyrene) | Amorphous | Tg about 100°C | 180 to 250°C | Packaging, disposable items, housings |
Common plastics stay within the ranges above, but some high-performance plastics go much higher. PEEK melts at about 343°C, PTFE at about 327°C and PPS at about 280°C. PTFE is a special case. Its melt viscosity is so high that it does not flow like other thermoplastics and is usually shaped by sintering.
What Factors Affect Plastic Melting Point?
Several factors decide where a plastic melts or softens. Some come from the polymer itself, while others come from what is blended into it. This is why grades of the same plastic can have different processing temperatures.
- Molecular Structure and Crystallinity: Rigid, tightly packed chains and higher crystallinity raise the melting point. Flexible or branched chains lower it. This is why HDPE melts at a higher temperature than LDPE.
- Molecular Weight: Higher molecular weight increases melt viscosity and can raise the softening range slightly, which changes how easily the material flows during processing.
- Additives and Plasticizers: Plasticizers lower Tg and soften the material. Flexible PVC is a common example.
- Fillers and Reinforcement: Glass fiber and mineral fillers change the melting point very little, but they raise heat resistance under load and affect flow and shrinkage.
- Blends and Recycled Content: Mixed polymers can show more than one melting peak. Recycled material may also carry contaminants that shift the processing behavior.
How Plastic Melting Point Affects Manufacturing Processes
Melting point sets the temperature window for every melt-based process. Too little heat leaves the material unmelted and hard to shape. Too much heat causes degradation. Each process uses this window differently.
Injection Molding
In the injection molding process, barrel temperatures are set in stages, usually above the melting point for crystalline plastics and within the recommended range for amorphous plastics. Mold temperature is just as important. It controls cooling speed, crystallinity, shrinkage and surface finish. Crystalline materials such as nylon and PP tend to shrink more and need tighter mold temperature control. Materials with a narrow window, such as PVC, require careful control to avoid degradation.
Extrusion
Extrusion runs continuously, so a stable melt temperature along the barrel and at the die is essential for consistent output. Melt temperature also affects melt strength, which determines whether the extruded shape holds its form before cooling.
Blow Molding and Thermoforming
Blow molding requires a heated parison with enough melt strength to be inflated without tearing or sagging. Bottles and hollow containers are typical results. Thermoforming heats a sheet to a softened state rather than a full melt. Amorphous sheets have a wider forming range, while crystalline sheets such as PP have a narrow one, because the material goes from stiff to sagging within a small temperature change near the melting point. Trays, packaging and covers are common products.
Plastic Applications Based on Melting Point
Plastic selection varies across industries because each application has different temperature and performance requirements.
- Automotive Components: Plastics with good heat resistance are used for under-hood parts, electrical connectors, housings, and other components exposed to elevated temperatures.
- Consumer Electronics: Plastics are commonly used for housings, connectors, switches, and structural components where thermal stability and dimensional accuracy are important.
- Medical Applications: Plastics are used for medical device housings, diagnostic equipment components, and fluid-handling parts, where temperature resistance, chemical compatibility, sterilization conditions, and dimensional stability are important.
- Industrial Equipment: Higher-performance plastics may be selected for components exposed to heat, chemicals, mechanical loads, or demanding operating conditions.
- Robotics: Plastics are used for housings, gears, bushings, and other components where thermal performance, wear resistance, and dimensional stability are required.
Need Help Choosing the Right Plastic for Custom Parts?
Not every plastic has a true melting point. Thermoset plastics and vulcanized rubber do not melt at all. Once cured, their cross-linked structure holds together until overheating causes decomposition, so they are shaped by curing rather than melting. This is why material selection should always be matched to the processing method, not based on temperature alone.
Jiangzhi provides custom plastic parts tailored to your material requirements, processing conditions, operating environment, and cost considerations. If you are unsure which material or process is right for your project, contact Jiangzhi for a professional evaluation and request a quote.
FAQs About Plastic Melting Point
Most common plastics do not melt in boiling water. At 100°C, materials such as PP, HDPE, nylon, and ABS stay solid, though some low-melting plastics can soften. Sunlight does not melt plastic either, but surfaces in direct sun can reach roughly 60 to 80°C. That is enough to warp thin or low-heat-resistance parts, and UV exposure can degrade the material over time.
When the temperature is too low, the melt is too thick, which leads to short shots, poor weld lines and weak parts. When it is too high, the material can degrade, turn yellow or brown, release gas, and produce flash. Uneven or poorly controlled cooling can cause sink marks and warpage. Staying within the recommended processing window is the simplest way to avoid these defects. The process sections above explain how the window differs by method.
Most different plastics do not blend well. They separate into distinct phases with weak bonding, which leads to brittleness and delamination. Different melting points add another problem, since one material may degrade before the other fully melts. Compatible pairs such as PC and ABS are the exception, and compatibilizers can improve others.
Compared with metals, plastic melting points are low. Common plastics melt or process between roughly 100°C and 300°C, while aluminum melts at 660°C. High performance plastics such as PEEK reach about 343°C, which is still lower than most metals. The table in the common plastics section lists typical values for widely used materials.
Melting point is the temperature at which a plastic transitions into a molten state, mainly describing its melting behavior during processing. Heat deflection temperature (HDT) indicates the temperature at which a plastic begins to deform under a specified load. For finished parts, HDT can be more relevant when heat and mechanical loads are involved.
