If you work with plastic raw materials—whether you are a product designer, injection molder, procurement engineer, or quality inspector—knowing the melting point or softening point of a plastic is one of the most fundamental pieces of information you need.
But “melting point” does not mean the same thing for every plastic. Some plastics melt like ice; others soften like butter. Understanding this difference is critical for material selection, processing, and end-use performance.
This guide also connects to detailed material pages for buyers who need deeper data. If you are comparing PC, ABS, or PP, you can continue to our guides on polycarbonate melting point, ABS melting point, and PP melting point for material-specific processing details.
This complete guide explains:
- What “melting point” really means for plastics
- The difference between crystalline melting point and amorphous softening point
- Melting and softening point data for common plastic raw materials
- How melting behavior affects injection molding and extrusion
- Links to detailed guides for each plastic material
1. Melting Point vs. Softening Point: Crystalline vs. Amorphous Plastics
Plastics are broadly divided into two categories based on their molecular structure:
| Type | Molecular Structure | Melting Behavior | Examples |
|---|---|---|---|
| Semi-crystalline | Ordered, packed molecular chains | True melting point (Tm) | PP, PA6, PA66, POM, PBT, HDPE |
| Amorphous | Random, disordered molecular chains | No true melting point; softens over a range | ABS, PC, PMMA, PS |
Semi-crystalline plastics have a true melting point
These materials have regions of highly ordered molecular chains, called crystallites. When heated, the crystallites break down at a specific temperature, causing the material to transition from solid to liquid. This temperature is called the melting point (Tm) and is typically sharp, often within a few degrees.
Examples:
- PP melts at about 160–170°C.
- PA66 melts at about 255–265°C.
Amorphous plastics do not have a melting point
Amorphous plastics have no crystalline structure. Instead of melting, they gradually soften as temperature rises. The most important thermal transition is the glass transition temperature (Tg), where the material changes from a hard, glassy state to a rubbery state. Another practical measurement is the Vicat softening point, which indicates the temperature at which a needle penetrates the surface under load.
Examples:
- ABS has a Tg of about 105°C and a Vicat softening point of 95–110°C.
- PC has a Tg of about 147°C and a Vicat softening point of 145–150°C.
For amorphous engineering plastics, PC and ABS are two common examples where “melting point” is often misunderstood. The polycarbonate melting point article explains why PC should be judged by Tg, Vicat softening temperature, heat resistance, and processing window. The ABS melting point guide gives a similar explanation for ABS softening range, Vicat data, and injection molding temperature.
Practical takeaway:
If a datasheet lists a “melting point” for an amorphous plastic, it usually refers to the Vicat softening point, softening range, or processing temperature. It is not a true phase transition.
2. Complete Melting Point and Softening Point Data Table
The table below summarizes key thermal properties for common plastic raw materials.
All values are typical ranges for unfilled, general-purpose grades. Actual data may vary by grade, filler content, manufacturer, and test method.
| Material | Type | Melting Point (Tm) | Glass Transition (Tg) | Vicat Softening Point | HDT @ 1.8 MPa | Typical Processing Temp. |
|---|---|---|---|---|---|---|
| ABS | Amorphous | No true Tm | ~105°C | 95–110°C | 85–100°C | 200–250°C |
| PC | Amorphous | No true Tm | ~147°C | 145–150°C | 125–140°C | 280–320°C |
| PP | Semi-crystalline | 160–170°C | ~-10°C | — | 50–110°C | 200–250°C |
| PA6 | Semi-crystalline | 220–225°C | 50–60°C | — | 60–100°C | 240–270°C |
| PA66 | Semi-crystalline | 255–265°C | 50–70°C | — | 70–100°C | 270–300°C |
| POM | Semi-crystalline | 165–185°C | -60 to -80°C | — | 110–125°C | 190–230°C |
| PBT | Semi-crystalline | 220–225°C | 40–60°C | — | 50–85°C | 240–270°C |
| PMMA | Amorphous | No true Tm | ~105°C | 95–110°C | 75–95°C | 220–250°C |
| HDPE | Semi-crystalline | 120–140°C | ~-110°C | — | 45–60°C | 180–240°C |
| PS | Amorphous | No true Tm | ~100°C | 90–100°C | 70–90°C | 180–260°C |
Note:
HDT = Heat Deflection Temperature at 1.8 MPa load. “—” indicates the property is not typically reported for that material.
When using this table for resin comparison, do not compare melting point alone. For PC resin selection, buyers should also review the PC resin datasheet to check Tg, Vicat softening temperature, HDT, impact strength, melt flow rate, and processing conditions together.
3. Detailed Material Profiles
Below are short profiles for common plastic raw materials. Each material has different melting behavior, processing temperature, and end-use performance.
ABS: Amorphous, No True Melting Point
ABS softens rather than melts. Its glass transition temperature is about 105°C, and its Vicat softening point is usually 95–110°C.
Typical injection molding temperature is 200–250°C.
ABS is an amorphous resin, so its heat behavior is better judged by softening range, Vicat temperature, and molding conditions. Our ABS melting point guide explains these values in more detail.
PC: Amorphous, No True Melting Point
For PC resin, buyers should not treat melting point as a single fixed value. See our detailed guide to polycarbonate melting point to understand Tg, softening behavior, processing temperature, and heat resistance.Polycarbonate has a high Tg of about 147°C and a Vicat softening point of 145–150°C.
It needs high processing temperatures, usually 280–320°C.
For PC resin, buyers should not treat melting point as a single fixed value. See our detailed guide to polycarbonate melting point to understand Tg, softening behavior, processing temperature, and heat resistance.
PP: Semi-crystalline, Tm 160–170°C
Unlike ABS and PC, PP is a semi-crystalline resin with a clearer crystalline melting range. Read our PP melting point guide for homopolymer PP, random copolymer PP, impact copolymer PP, HDT, and processing temperature.
It melts sharply at 160–170°C and is usually processed at 200–250°C.
PA6: Semi-crystalline, Tm 220–225°C
Nylon 6 melts at about 220–225°C.
It absorbs moisture, which can affect drying, melt flow, surface quality, and final part performance.
PA66: Semi-crystalline, Tm 255–265°C
Nylon 66 has a higher melting point than PA6.
Its Tm is usually 255–265°C, making it suitable for higher-temperature applications.
POM: Semi-crystalline, Tm 165–185°C
Acetal, also called POM, has a sharp melting point between 165–185°C.
It is widely used when dimensional stability, low friction, and good wear resistance are required.
PBT: Semi-crystalline, Tm 220–225°C
PBT melts at a similar temperature to PA6, usually 220–225°C.
Compared with nylon, it has lower water absorption and faster crystallization.
PMMA: Amorphous, No True Melting Point
PMMA, also known as acrylic, does not have a true melting point.
It softens at about 95–110°C by Vicat measurement and is usually processed at 220–250°C.
HDPE: Semi-crystalline, Tm 120–140°C
HDPE is a semi-crystalline polyethylene material with a melting point of about 120–140°C.
It is commonly processed at 180–240°C and is widely used for bottles, containers, pipes, films, and industrial parts.
PS: Amorphous, No True Melting Point
Polystyrene is an amorphous plastic. It does not have a true melting point.
Its Tg is about 100°C, and its Vicat softening point is usually 90–100°C.
4. How Melting Point Affects Plastic Processing
Knowing the melting point or softening point is only the first step.
You also need to understand how these values affect injection molding, extrusion, cooling, shrinkage, and part quality.
For Semi-crystalline Plastics
Examples include PP, PA6, PA66, POM, PBT, and HDPE.
For these materials, the barrel temperature should be set above Tm. In many cases, it is set about 20–50°C higher than the melting point.
This helps ensure complete melting and stable flow.
Mold temperature is also important. It controls the crystallization rate of the polymer.
A higher mold temperature can improve crystallinity and dimensional stability, but it may also increase cycle time.
Cooling time is affected by the difference between melt temperature and mold temperature.
Semi-crystalline plastics usually have higher shrinkage than amorphous plastics. Mold design must allow for this shrinkage.
For Amorphous Plastics
Examples include ABS, PC, PMMA, and PS.
These plastics do not have a true melting point. Their processing temperature is selected well above the Vicat softening point to achieve enough melt flow.
Mold temperature is usually kept below Tg. This helps the part cool and demold without serious distortion.
Amorphous plastics usually have lower and more predictable shrinkage than semi-crystalline plastics.
General Processing Rule
Always check the material supplier’s recommended processing window.
The values in this guide are typical ranges. Specific grades, especially glass-filled, mineral-filled, flame-retardant, or high-flow grades, may need different settings.
5. Frequently Asked Questions
What is the difference between melting point and glass transition temperature?
The melting point, or Tm, is the temperature at which the crystalline regions of a semi-crystalline polymer break down and the material becomes liquid.
The glass transition temperature, or Tg, is the temperature at which an amorphous polymer changes from a hard, glassy state to a softer, rubbery state.
Amorphous plastics do not have a true Tm. They have Tg, Vicat softening point, and processing temperature ranges.
Which plastic in this guide has the highest melting point?
Among the plastics listed in this guide, PA66 has the highest melting point, about 255–265°C.
PA6 and PBT follow with melting points of about 220–225°C.
Can amorphous plastics melt?
Amorphous plastics such as ABS, PC, PMMA, and PS do not have a true melting point.
They soften gradually as temperature increases.
The term “melting point” is sometimes used incorrectly for amorphous plastics. In most cases, it refers to Vicat softening point, softening range, or processing temperature.
Why do semi-crystalline plastics have a sharp melting point?
Semi-crystalline plastics contain ordered crystalline regions.
These regions need a specific amount of heat energy to break down.
Once this energy level is reached, the material changes quickly from solid to molten state. This creates a sharper melting range.
How does melting point affect mold temperature selection?
For semi-crystalline plastics, mold temperature affects crystallinity, shrinkage, warpage, and mechanical properties.
If the mold temperature is too low, the material may not crystallize properly. This can cause warpage, unstable dimensions, or weaker parts.
For amorphous plastics, mold temperature mainly affects cooling rate, internal stress, surface quality, and demolding.
What happens if an amorphous plastic is processed above its decomposition temperature?
Processing above the decomposition temperature can cause thermal degradation.
Common problems include discoloration, reduced mechanical strength, poor surface quality, gas marks, and volatile release.
Always process the resin within the supplier’s recommended temperature range.
6. Data Sources and Disclaimer
The data in this guide are typical values compiled from public material datasheets, technical data sheets, ISO 10350, ASTM D3418, UL Prospector, and CAMPUS material databases.
Actual thermal properties may vary by grade, manufacturer, filler content, additive package, and test conditions.
For critical applications, always verify the exact thermal properties from the material supplier’s official datasheet.
