ABS, PP, PE, PC, Nylon: Recommended Mold Temperatures for Common Plastics
Mold temperature is one of the most influential variables in injection molding and plastic processing. Set it correctly, and you get glossy surfaces, proper dimensional stability, and consistent part quality. Set it wrong, and you get sink marks, warping, short shots, and surface defects that render parts worthless.
Different plastics have dramatically different temperature requirements. Polypropylene wants to be kept relatively cool to prevent warping. Polycarbonate needs significant heat to flow properly into thin-wall sections. Nylon absorbs moisture from the air and needs careful drying and stable temperature control to avoid splay and blistering.
This reference guide provides recommended mold temperatures for the most common industrial plastics — PP, PE, ABS, PC, PA, PVC, PMMA, PBT, and POM — along with the reasoning behind each recommendation. Bookmark this page: it is the most-searched reference table in the plastic processing industry.
The mold surface temperature directly controls:
The mold temperature controller (MTC) is the tool that maintains these temperatures. ZILLION offers water-type MTCs (ZLW series, max 120°C) for standard applications and oil-type MTCs (ZLO series, max 180°C) for high-temperature engineering plastics.
| Material | Full Name | Typical Mold Temp (°C) | MTC Type | Notes |
|---|---|---|---|---|
| PP | Polypropylene | 20 - 40 | Water (ZLW) | Low mold temp needed to prevent warpage. Low thermal conductivity of PP makes temperature control less critical. |
| HDPE | High-Density Polyethylene | 40 - 60 | Water (ZLW) | Moderate temps. HDPE crystallizes slowly — too high mold temp causes post-molding warpage. |
| LDPE | Low-Density Polyethylene | 30 - 50 | Water (ZLW) | Similar to HDPE. Lower mold temps reduce cycle time. |
| ABS | Acrylonitrile Butadiene Styrene | 50 - 80 | Water (ZLW) | Temperature-sensitive. Below 40°C causes poor surface finish and excessive gloss variation. 60°C+ for high-quality cosmetic parts. |
| PC | Polycarbonate | 80 - 120 | Oil (ZLO) preferred above 100°C | High mold temp critical for flow in thin-wall applications. PC absorbs moisture — dry to <0.02% before molding. |
| PA6 (Nylon 6) | Polyamide 6 | 60 - 100 | Oil (ZLO) preferred | Highly hygroscopic. Moisture causes splay, blistering. Dry thoroughly + stable temperature critical. |
| PA66 (Nylon 66) | Polyamide 66 | 70 - 110 | Oil (ZLO) preferred | Higher mold temp than PA6. Temperature variations cause property inconsistency between shots. |
| PVC (rigid) | Polyvinyl Chloride | 40 - 60 | Water (ZLW) | Thermal degradation risk — avoid excessive temperature. Mold cooling is more critical than heating. |
| PMMA | Polymethyl Methacrylate (Acrylic) | 60 - 80 | Water (ZLW) | Surface finish critical — temperature variations visible as flow marks. Tight ±2°C control needed for optical quality. |
| PBT | Polybutylene Terephthalate | 60 - 100 | Oil (ZLO) preferred | Engineering plastic. Higher mold temps reduce sink marks in thick sections. |
| POM (Acetal) | Polyoxymethylene | 60 - 100 | Water or Oil (ZLW/ZLO) | Low thermal expansion. Tight mold temp control reduces dimensional variation. |
| PS | Polystyrene | 40 - 60 | Water (ZLW) | General-purpose. Low mold temps reduce cycle time. Too high causes brittleness in thin sections. |
| HIPS | High-Impact Polystyrene | 40 - 60 | Water (ZLW) | Similar to PS. The rubber modifier in HIPS makes it more tolerant of temperature variation. |
| PET | Polyethylene Terephthalate | 80 - 120 | Oil (ZLO) preferred | Crystallization-sensitive. Too low mold temp causes hazy parts. Must be processed above 70°C for proper crystallization. |
| PBT+PET (Blend) | PBT/PET Alloy | 70 - 100 | Oil (ZLO) preferred | Balance of PET crystallization and PBT flow. Temperature variation causes property inconsistency. |
| TPU | Thermoplastic Polyurethane | 20 - 50 | Water (ZLW) | Highly elastic. Lower mold temps prevent sticking. Some grades require heated molds for release. |
| PEEK | Polyether Ether Ketone | 160 - 200 | Oil (ZLO) 180°C+ required | High-performance. Requires dedicated high-temp MTC (ZLO series). Mold temp critical for crystallinity and mechanical properties. |
| PP+GF (Glass-Filled) | PP Reinforced with Glass Fiber | 40 - 80 | Water (ZLW) | Higher mold temp than unfilled PP reduces glass fiber orientation and warpage. |
Mold temperature and melt temperature are two separate variables, though they interact. The melt temperature is the temperature of the plastic as it enters the mold (typically 20-40°C above the mold surface temperature for most materials). The mold surface temperature is what the MTC actually controls.
General rule: the mold should be hot enough to allow the material to fill the cavity completely without freezing off, but cool enough to solidify the part within a reasonable cycle time. Increasing mold temperature generally:
Most standard plastics (PP, PE, ABS, PS) process perfectly well with water-type mold temperature controllers (ZILLION ZLW series, max 120°C). For engineering plastics and high-temperature applications, an oil-type MTC (ZILLION ZLO series, max 180°C) is required:
| Application | Required Mold Temp | Recommended MTC |
|---|---|---|
| PP, PE, PS, ABS, PVC, PMMA | 20 - 80°C | Water MTC (ZLW series, max 120°C) |
| PC, PA, PBT, PET, POM (standard) | 60 - 120°C | Water MTC sufficient up to 120°C; Oil MTC preferred for above 100°C |
| High-temp PC, filled compounds | 100 - 160°C | Oil MTC (ZLO series, max 180°C) required |
| PEEK, high-performance resins | 160 - 200°C | High-temp oil MTC or dedicated heating system |
Having the right target temperature is only part of the equation. Temperature stability — the MTC's ability to hold the setpoint consistently — matters equally. A mold that swings between 55°C and 65°C (a ±5°C variation) will produce parts with inconsistent dimensions and surface quality, even if the average temperature is correct.
Key factors affecting temperature stability:
Several of the most temperature-demanding plastics are also highly moisture-sensitive. Attempting to process them without proper drying causes immediate quality problems:
| Material | Moisture Sensitivity | Required Dry Time | Drying Temp | Max Moisture Content |
|---|---|---|---|---|
| PC | High | 3 - 4 hours | 120°C | <0.02% |
| PA6 (Nylon) | Very High | 4 - 6 hours | 80 - 100°C | <0.10% |
| PA66 | Very High | 4 - 6 hours | 80 - 100°C | <0.10% |
| PET | High | 4 - 6 hours | 130 - 150°C | <0.02% |
| ABS | Medium | 2 - 4 hours | 80°C | <0.05% |
| PBT | Medium | 3 - 4 hours | 120°C | <0.02% |
Use a hopper dryer for continuous drying during production. Never allow hygroscopic materials to sit exposed to ambient air — they reabsorb moisture within 30-60 minutes.
| Defect | Temperature Cause | Fix |
|---|---|---|
| Sink marks | Mold temp too high (material too fluid, thick sections shrink after skin solidifies) | Reduce mold temp 5-10°C, or increase holding pressure/time |
| Warpage | Non-uniform mold temperature causing uneven shrinkage | Check cooling channel balance, ensure uniform mold temp across cavity, reduce ejection temp |
| Short shot | Mold temp too low (material freezes before cavity fills) | Increase mold temp 10-20°C, check material melt temp |
| Flow marks / poor surface | Mold temp too low for material to fill and pack properly | Increase mold temp 10-20°C, especially for cosmetic parts |
| Flash | Mold temp too high (material viscosity too low, enters parting line gaps) | Reduce mold temp 5-10°C, reduce injection pressure |
| Splay / silver streaks | Moisture in hygroscopic material (not mold temp issue — check drying) | Dry material properly before processing. Check hopper dryer operation. |
| Dimensional variation | Temperature fluctuation between shots or between cavities | Run P.I.D. auto-tune on MTC. Check cooling channel flow balance. |
Q: Can I use a water MTC for polycarbonate?
A: For PC parts requiring mold temperatures up to 120°C, a water MTC (ZILLION ZLW series) is technically sufficient. However, above 90-100°C, water MTCs experience higher pressure and boiling risk. For PC applications above 100°C mold temperature, an oil MTC (ZLO series, max 180°C) is strongly recommended for safety and stability.
Q: How do I know if my mold temperature is actually correct?
A: The most reliable method is to use a contact or infrared thermometer to measure the mold surface temperature directly at the cavity during a production run. Compare this to your target setpoint. If there is a consistent gap (e.g., setpoint 60°C but mold surface reads 52°C), your MTC may be undersized, or there may be a flow restriction in the cooling circuit.
Q: What happens if mold temperature is too high?
A: Excessive mold temperature causes sink marks (especially in thick sections), flash at the parting line, extended cycle times, and in extreme cases, material degradation. It can also cause part ejection difficulties if the surface becomes too sticky.
Q: What is the most common mold temperature mistake?
A: Running the mold too cold. Operators often err on the side of low mold temperatures to reduce cycle time, but this causes a cascade of quality problems — warpage, short shots, poor surface finish, and dimensional inconsistency — that are more costly than the cycle time saved.
Q: Should mold temperature be the same for both halves of the mold?
A: Ideally yes — but in practice, many molds have different cooling requirements for the core and cavity sides. A temperature difference of up to 10-15°C between core and cavity is sometimes intentional to control differential shrinkage in specific part geometries. Document your stable operating temperatures once established.
Getting mold temperatures right is fundamental to quality plastic processing. This guide covers the recommended temperatures for the most common industrial plastics — but these are starting points. Your specific grade, part geometry, tooling, and quality requirements may require fine-tuning.
The key principles to remember: match your MTC type to your temperature requirement (water vs oil), dry hygroscopic materials properly, run P.I.D. auto-tune when changing molds, and measure actual mold surface temperature rather than relying solely on the MTC display.
ZILLION offers a complete range of mold temperature controllers — water type (ZLW, max 120°C) and oil type (ZLO, max 180°C) — plus hopper dryers for material drying. Contact our technical team for MTC sizing and application support for your specific material and part requirements.
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