PP has a true crystalline melting point, but melting point is not the same as heat resistance. Homopolymer PP usually melts at 160–170°C, random copolymer PP at about 130–155°C, and impact copolymer PP at 150–165°C.
For real part performance, you should also check HDT, load, MFI, shrinkage, processing temperature, and the exact TDS of the grade you buy.
PP Has a Clear Melting Point, But You May Be Using the Wrong Data
Unlike amorphous plastics such as ABS and PC, PP is a semi-crystalline plastic with a true crystalline melting point. Homopolymer PP usually melts at 160–170°C, and this value is relatively stable across technical sources.
But this is not the real issue.
The real issue is that many users treat melting point as the answer to this question:
“How much heat can PP withstand?”
That is the wrong way to read the data.
Melting point only tells you when PP changes from a solid crystalline structure into a melt. It does not tell you whether a molded part can keep its shape under load.
For many unfilled homopolymer PP grades, HDT at 1.8 MPa is only about 50–60°C. This means a PP part may start to deform under load far below its melting point.
So the practical rule is simple:
- If the part is exposed to heat only, melting point and short-term heat resistance matter.
- If the part is exposed to heat plus load, HDT and dimensional stability matter more.
- If the part needs to fill a mold, MFI and processing temperature matter more than melting point.
PP has a true crystalline melting point, while ABS only has a softening range. However, PP can still deform under load at a lower temperature than many users expect.
This article explains PP melting point, HDT, softening behavior, processing temperature, and grade selection in one guide.
Direct Answer: What Is the Melting Point of PP?
The melting point of PP depends mainly on the polymer type, ethylene content, crystallinity, and additives.
The three most common PP types have the following melting ranges:
| PP Type | Melting Point / Tm | Key Characteristics | Common Applications |
|---|---|---|---|
| Homopolymer PP | 160–170°C | Highest rigidity, good chemical resistance, low cost | Injection molded parts, raffia, woven bags, sheets |
| Random Copolymer PP | 130–155°C | Better transparency, flexibility, and heat sealability | Food containers, medical packaging, transparent films |
| Impact / Block Copolymer PP | 150–165°C | Better low-temperature impact, balanced stiffness and toughness | Automotive parts, appliance housings, crates, pipes |
Important note: melting point and heat resistance are different. Homopolymer PP has the highest melting point, but many unfilled grades still have low HDT under high load.
Also, random copolymer PP should not be confused with PP-R pipe grade. PP-R pipe materials are random copolymer grades designed for pressure pipe systems and long-term hot-water use. Not every random copolymer PP is suitable for hot water pipes.
Why Melting Point Is Not the Same as Heat Resistance
Melting point is the temperature where PP crystals break down and the material becomes a melt.
HDT, or heat deflection temperature, measures when a plastic specimen starts to bend under a defined load.
This difference is critical in real applications.
A PP food container may survive microwave heating because the container is exposed to short-term heat with little load. But a PP structural bracket in a hot environment may deform because it carries load while temperature rises.
This is why you should never judge PP heat resistance by melting point alone.
| Data Point | What It Means | Why It Matters |
|---|---|---|
| Melting Point / Tm | Temperature where crystalline PP melts | Useful for understanding polymer type and processing window |
| HDT | Temperature where the part deforms under load | Critical for structural parts exposed to heat |
| Vicat Softening Temperature | Softening behavior under needle penetration load | Useful for comparing thermal softening |
| Processing Temperature | Barrel or melt temperature used in molding | Controls flow, filling, surface quality, and degradation risk |
For standard unfilled PP, the melting point may be above 160°C, but the useful temperature under load can be much lower.
Filled PP is different. Talc-filled or glass-fiber-reinforced PP can deliver higher stiffness, better dimensional stability, and much higher HDT. This is why filled PP is often used in automotive interior parts, appliance housings, and structural components.
Why Do Different PP Grades Have Different Melting Points?
Different PP grades have different melting points because their molecular structures are different.
PP is made from propylene monomers. Pure homopolymer PP has regular molecular chains and higher crystallinity. This gives it the highest melting point.
But homopolymer PP has one weakness: low-temperature brittleness. Below 0°C, many homopolymer PP grades become brittle and lose impact strength.
To improve flexibility, transparency, or low-temperature impact resistance, producers introduce ethylene during polymerization.
1. Homopolymer PP
Homopolymer PP contains only propylene monomers.
It has:
- Higher crystallinity
- Higher rigidity
- Higher tensile strength
- Higher melting point
- Lower low-temperature impact resistance
Typical melting point:
160–170°C
Homopolymer PP is widely used for rigid injection molded parts, sheets, raffia, woven bags, and general-purpose applications.
2. Random Copolymer PP
Random copolymer PP contains a small amount of ethylene randomly distributed along the polymer chain.
This disrupts crystallinity and lowers the melting point. It also improves clarity, flexibility, and heat sealability.
Typical melting point:
130–155°C
Random copolymer PP is commonly used in transparent packaging, food containers, medical packaging, films, and heat-sealing applications.
3. Impact / Block Copolymer PP
Impact copolymer PP contains a rubber phase dispersed in the PP matrix.
This improves low-temperature impact resistance and toughness. The melting point is usually lower than homopolymer PP but higher than many transparent random copolymer grades.
Typical melting point:
150–165°C
Impact copolymer PP is used in automotive parts, appliance housings, crates, battery cases, industrial parts, and impact-resistant molded products.
4. PP-R and PP-RCT Pipe Grades
PP-R is a polypropylene random copolymer pipe grade designed for pressure pipe systems.
PP-RCT is a polypropylene random copolymer with modified crystallinity. It is designed for better pressure resistance at elevated temperature.
These pipe grades should not be selected only by melting point. For hot water and pressure pipe applications, check:
- Pipe grade certification
- Long-term hydrostatic strength
- Pressure rating
- Standard compliance
- Thermal aging resistance
- Supplier TDS and test reports
For long-term hot water use, grade certification is more important than a generic PP melting point value.
Why Do Datasheets Show Different PP Melting Points?
You may see different PP melting point values in different datasheets or technical articles.
This does not always mean one source is wrong.
The difference may come from:
- Different DSC test methods
- Different ethylene content
- Different crystallinity
- Different nucleating agents
- Different fillers
- Different stabilizer packages
- Different measurement or reporting methods
For material selection, do not rely only on a generic value such as “PP melts at 160°C.”
Always use the TDS of the exact grade you buy.
This is especially important for transparent PP, impact copolymer PP, filled PP, and pipe-grade PP.
What Type Are the PP Grades You Buy?
The following are typical PP brands and grades we distribute, grouped by type for quick reference.
Values are typical ranges. Please confirm the latest TDS before final material approval.
Homopolymer PP Grades
| Brand | Grade | Tm | MFI | Typical Applications |
|---|---|---|---|---|
| Formosa Tairipro® | K1011 | 160–165°C | 1.5 g/10 min, 230°C/2.16 kg | Extrusion, sheets, pipes |
| Formosa Tairipro® | K1023 | 160–165°C | 11 g/10 min, 230°C/2.16 kg | General purpose injection molding |
| Formosa Tairipro® | K1035 | 160–165°C | 35 g/10 min, 230°C/2.16 kg | Thin-wall injection molding |
| Formosa YUNGSOX® | 3080 | 160–165°C | 8 g/10 min, 230°C/2.16 kg | General purpose injection molding |
| Formosa YUNGSOX® | 3204 | 160–165°C | 20 g/10 min, 230°C/2.16 kg | High flow, thin-wall parts |
| Sinochem Fuya® | L5E89 | 160–165°C | 3.4 g/10 min, 230°C/2.16 kg | Raffia, woven bags |
| Sinochem Fuya® | H3030F | 160–165°C | 30 g/10 min, 230°C/2.16 kg | Film, fiber |
Impact / Block Copolymer PP Grades
| Brand | Grade | Tm | MFI | Typical Applications |
|---|---|---|---|---|
| Formosa Tairipro® | 7523 | 155–163°C | 11 g/10 min, 230°C/2.16 kg | Automotive parts, impact-resistant molded parts |
| Formosa Tairipro® | 7633 | 155–163°C | 25 g/10 min, 230°C/2.16 kg | High-flow impact-resistant parts |
| Formosa YUNGSOX® | 7433 | 155–163°C | 25 g/10 min, 230°C/2.16 kg | General-purpose impact copolymer applications |
| Lotte Starex® | ABF-6220 | 155–163°C | 20 g/10 min, 230°C/2.16 kg | Automotive parts, appliance housings |
| CNOOC Shell Davance® | EP548R-Z | 155–163°C | 8 g/10 min, 230°C/2.16 kg | Automotive parts, high-stiffness molded parts |
Transparent Random Copolymer PP Grades
| Brand | Grade | Tm | MFI | Typical Applications |
|---|---|---|---|---|
| Lotte Starex® | VI-6120N | 130–145°C | 12 g/10 min, 230°C/2.16 kg | Transparent packaging, medical packaging |
| Lotte Starex® | VI-6220N | 130–145°C | 20 g/10 min, 230°C/2.16 kg | High-flow transparent thin-wall parts |
| Lotte Starex® | VP-6020NH | 130–145°C | 20 g/10 min, 230°C/2.16 kg | High-transparency, high-gloss packaging |
How to Read These Grade Tables
Do not select PP only by melting point.
There is no direct correlation between melting point and HDT. When selecting PP, first decide whether your part is exposed to heat only or heat plus load.
If your part only sees short-term heat, PP may be suitable. This includes microwave food containers and some hot-fill packaging.
If your part carries load at elevated temperature, check HDT, stiffness, creep resistance, and dimensional stability. Standard unfilled PP may not be enough.
MFI is also critical.
Homopolymer PP can have a wide MFI range, from low-flow extrusion grades to high-flow thin-wall injection grades. In many molding projects, MFI is more important than melting point.
For transparent PP, the melting point is usually lower. But transparent packaging often does not require high load-bearing heat resistance, so this trade-off is acceptable.
Processing Temperature of PP: Why 200–250°C?
PP melts at around 160–170°C for homopolymer grades, but injection molding barrel temperatures are usually set between 200°C and 250°C.
This is because melting point only tells you when the crystalline structure breaks down. It does not mean the melt already has enough flowability to fill the mold.
To reduce melt viscosity and fill the cavity smoothly, PP needs a higher processing temperature than its melting point.
Typical injection molding parameters:
| Parameter | Recommended Value | Notes |
|---|---|---|
| Drying temperature | Usually not required for unfilled PP | Unfilled PP has very low water absorption. Filled or recycled grades may need drying. |
| Barrel temperature | 200 → 220 → 230–250°C | Use rear-to-front temperature control. Avoid excessive melt temperature. |
| Mold temperature | 20–50°C | Low mold temperature shortens cycle time but may increase warpage. |
| Back pressure | 5–15 bar | Helps improve melt uniformity. |
| Screw speed | 60–150 rpm | Medium to high screw speed is common because PP has relatively low viscosity. |
PP degradation risk increases significantly above 270°C, especially with long residence time, oxygen exposure, or high shear.
Avoid barrel temperatures above 270°C unless the TDS specifically allows it. Purge the machine before shutdown.
Use local ventilation when processing PP at high melt temperatures, especially when using recycled, filled, pigmented, or flame-retardant grades.
Common PP Processing Problems
1. Warpage and Shrinkage
PP is a semi-crystalline plastic. Its molding shrinkage is usually much higher than amorphous plastics.
Typical shrinkage can reach 1.0–2.5%, depending on grade, mold design, wall thickness, and processing conditions.
During cooling, crystallization causes volume shrinkage. Uneven mold temperature can increase warpage.
Common solutions:
- Optimize cooling channel design
- Keep mold temperature uniform
- Increase mold temperature moderately when needed
- Avoid large wall-thickness differences
- Use proper packing pressure and packing time
- Consider filled PP if dimensional stability is critical
2. Sink Marks
PP has relatively high shrinkage, so thick sections are prone to sink marks.
Common solutions:
- Increase packing pressure
- Extend packing time
- Improve gate size and gate location
- Reduce thick wall sections
- Use rib design instead of solid thick sections
3. Thermal Degradation
PP can degrade when melt temperature is too high or residence time is too long.
Possible signs include:
- Yellowing or discoloration
- Black spots
- Odor
- Poor surface quality
- Reduced impact strength
- Increased brittleness
Common solutions:
- Keep melt temperature within the recommended range
- Avoid long residence time
- Purge before machine shutdown
- Reduce excessive screw speed or shear
- Check stabilizer package for high-temperature applications
Typical Applications Based on PP Heat Behavior
PP grade selection should be based on the actual temperature, load, and application environment.
| Application | Recommended PP Type | Why It Works |
|---|---|---|
| Microwave food containers | Food-contact PP or random copolymer PP | Suitable for short-term heat exposure with low mechanical load. |
| Woven bags and raffia | Homopolymer PP | High stiffness, good drawability, low density, and low cost. |
| Transparent packaging | Random copolymer PP | Better clarity, flexibility, gloss, and heat sealability. |
| Automotive interior trim | Impact copolymer PP or filled PP | Better balance of impact strength, stiffness, and dimensional stability. |
| Appliance housings | Impact copolymer PP or reinforced PP | Improved toughness and better resistance to deformation. |
| Hot water pipes | PP-R or PP-RCT pipe grade | Designed for long-term hot-water exposure and pressure pipe systems. |
| Battery cases | Impact copolymer PP | Good chemical resistance and improved impact performance. |
Quick Material Selection Guide: When Is PP Suitable?
PP is an excellent material when you need low density, chemical resistance, easy processing, and low cost.
But it is not suitable for every heat-related application.
| Actual Service Condition | Recommended Material | Reason |
|---|---|---|
| Room temperature, chemical contact, low cost | PP | Good chemical resistance, low density, and economical processing. |
| Long-term hot water, 70–95°C | PP-R or PP-RCT pipe grade | Designed for long-term hot-water exposure and pressure resistance. |
| Microwave heating, about 100–120°C short term | Food-contact PP grade | Suitable for short-term heating under proper use conditions. |
| Heat plus load, above 60°C | Standard unfilled PP is not recommended | Many unfilled PP grades have low HDT at 1.8 MPa. |
| Long-term heat plus load, above 80°C | PA66, POM, reinforced PP, or other engineering plastics | Higher HDT and better dimensional stability may be needed. |
| Low-temperature impact, below -20°C | Impact copolymer PP or PA66 | Homopolymer PP may become brittle at low temperature. |
Typical Case 1: Microwave Food Containers
Microwave food containers are a common PP application.
During heating, food temperature may reach around 100–120°C. But the container usually does not carry high mechanical load.
In this case, food-contact PP can work well under proper use conditions because the exposure is short term and the load is low.
However, avoid:
- Grill mode
- Oven heating
- High-oil heating
- Empty heating
- Reusing damaged containers
- Using non-food-contact recycled PP
For food-contact applications, always check the grade’s compliance documents and supplier TDS.
Typical Case 2: PP Structural Bracket Failure
A customer used unfilled homopolymer PP for a structural bracket near a high-temperature area.
The part looked suitable on paper because the PP melting point was above 160°C. But the bracket deformed during summer use.
The actual condition included:
- Ambient heat around 80–100°C
- Continuous mechanical load
- Vibration
- Limited dimensional tolerance
The problem was not melting. The problem was heat deflection under load.
In this case, unfilled homopolymer PP was not suitable. Better options include:
- Glass-fiber-reinforced PP
- PA66 + glass fiber
- POM
- Other engineering plastics with higher HDT
This is why HDT must be checked for structural parts exposed to heat.
What Should You Ask Before Buying PP Resin?
Do not rely only on general names such as “injection grade PP” or “food grade PP.”
Before buying PP resin, ask your supplier these questions:
- Is it homopolymer PP, random copolymer PP, impact copolymer PP, PP-R, or PP-RCT?
- What is the MFI at 230°C/2.16 kg?
- What is the melting point or DSC melting range?
- What is the HDT at 0.45 MPa and 1.8 MPa?
- What is the Vicat softening temperature?
- What is the recommended barrel temperature and mold temperature?
- What is the molding shrinkage range?
- Does it contain talc, glass fiber, nucleating agent, UV stabilizer, antistatic agent, or other additives?
- Is it suitable for food contact, medical packaging, hot water pipe, or outdoor use?
- Can the supplier provide the latest TDS, COA, SDS, and compliance documents?
These questions help you avoid wrong material selection, molding defects, deformation, and compliance risks.
Frequently Asked Questions
What is the actual melting point of PP?
Homopolymer PP usually melts at 160–170°C. Random copolymer PP usually melts at about 130–155°C. Impact or block copolymer PP usually melts at 150–165°C.
PP is a semi-crystalline plastic and has a true crystalline melting point. This is different from amorphous plastics such as ABS and PC, which do not have a true melting point.
Will PP melt in boiling water?
No. Boiling water is 100°C, which is far below the melting point of homopolymer PP.
However, standard PP may soften or deform during long-term exposure to hot water, especially under load.
For hot water pipe systems or long-term hot water contact, use certified PP-R or PP-RCT pipe grades rather than general-purpose PP.
Can PP be used in the microwave?
Yes, food-contact PP grades are commonly used for microwave containers and can tolerate short-term heating around 100–120°C under proper use.
However, avoid grilling, oven heating, high-oil heating, empty heating, or using non-food-contact recycled PP.
Always check whether the grade is approved for food-contact use.
Why is there such a big difference between PP melting point and HDT?
Melting point is the temperature where PP crystals melt.
HDT is the temperature where a plastic specimen bends under a defined load.
PP can lose stiffness far below its melting point because its molecular chains have mobility at normal use temperatures. This is why PP may deform under load at 60–80°C even though it does not melt until above 160°C.
How do I choose between homopolymer PP and copolymer PP?
Choose homopolymer PP when you need rigidity, chemical resistance, high tensile strength, and low cost.
Choose random copolymer PP when you need transparency, flexibility, gloss, or heat sealability.
Choose impact / block copolymer PP when you need low-temperature impact resistance, toughness, and better performance in automotive or appliance parts.
Choose PP-R or PP-RCT pipe grade when you need long-term hot water and pressure pipe performance.
Is PP-R the same as random copolymer PP?
PP-R is a type of random copolymer polypropylene designed for pressure pipe systems.
But not every random copolymer PP is PP-R.
For hot water pipe applications, you must check pressure rating, long-term hydrostatic strength, pipe standard compliance, and supplier certification.
Does glass fiber increase the melting point of PP?
Glass fiber does not significantly change the crystalline melting point of PP.
However, it can greatly improve stiffness, dimensional stability, and HDT. This is why glass-fiber-reinforced PP is used in automotive parts, appliance housings, brackets, and structural components.
Does PP need to be dried before processing?
Unfilled PP has very low water absorption and usually does not need drying.
However, filled PP, glass-fiber-reinforced PP, talc-filled PP, pigmented PP, or recycled PP may contain surface moisture.
In these cases, drying at 80–90°C for 2–3 hours may help prevent surface defects such as silver streaks.
What data should I check besides PP melting point?
Check:
- MFI
- HDT
- Vicat softening temperature
- Tensile strength
- Flexural modulus
- Impact strength
- Shrinkage
- Filler content
- Processing temperature
- Compliance documents
- Latest TDS and COA
For structural parts, HDT and stiffness are often more important than melting point.
For molding, MFI and shrinkage are often more important than melting point.
For regulated applications, compliance documents are as important as physical properties.
Need More Detailed PP Grade Data?
This article provides typical values for PP melting point, HDT, processing temperature, and grade selection.
If your application has special requirements for heat resistance, impact strength, flowability, transparency, food contact, medical packaging, or hot water performance, please contact us.
We can help you compare PP grades based on:
- Application temperature
- Load condition
- MFI requirement
- Mold structure
- Wall thickness
- Processing method
- Required compliance documents
- Target cost
We can also provide detailed TDS, COA, and grade recommendations for specific PP materials.
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