Last updated: 2026-09-02 · 5 min read

Which High-Temperature Resins Hold Up Under Continuous Heat — and How Do You Select Them?

High-temperature resins — PPS, PEEK, PEI, PPA, LCP — maintain mechanical properties above 150°C continuous use temperature, and selection depends on three parameters: the continuous use temperature (not the peak), the chemical environment, and the mechanical load at temperature. Choosing by peak temperature alone over-specifies the resin; choosing by continuous use temperature with the correct chemical and load data narrows the field to the grade that performs without overpaying for capability the part never needs.

Gate vestige — The visible mark left on the part surface where the gate was trimmed. Edge gate: 0.5–2.0mm vestige. Pin-point gate: 0.2–0.5mm. Valve gate: 0.05–0.1mm (flush). Vestige size affects cosmetic appearance and may require secondary trimming. See also related guide.

Key Facts

  • Continuous use temperature (RTI — Relative Thermal Index) is the rating that matters: PPS runs at 200–220°C, PEEK at 240–260°C, PEI at 170–180°C, PPA at 180–200°C, LCP at 200–240°C.
  • Melt processing temperature is much higher than use temperature: PEEK melts at 343°C and requires mold temperatures of 170–200°C; PPS requires 130–160°C mold temperature — these are not standard molding conditions and require specialized equipment.
  • Cost scales with performance: PPS is the most economical high-temp resin ($8–15/kg), PEEK is 5–10× more expensive ($80–150/kg) — the selection should justify the performance requirement, not default to the highest grade.

    • Gate vestige — The visible mark left on the part surface where the gate was trimmed. Edge gate: 0.5–2.0mm vestige. Pin-point gate: 0.2–0.5mm. Valve gate: 0.05–0.1mm (flush). Vestige size affects cosmetic appearance and may require secondary trimming. The related guide covers adjacent topics.

    High-Temperature Resin Comparison

    Resin RTI (°C) Key Strength Mold Temp (°C)
    PPS 200–220 Chemical resistance, dimensional stability 130–160
    PEEK 240–260 Mechanical strength at temperature, biocompatible grades 170–200
    PEI (Ultem) 170–180 Inherent flame resistance, transparent grades 175–200
    PPA 180–200 Balance of cost and performance, good chemical resistance 120–150
    LCP 200–240 Ultra-thin walls, SMT-compatible connectors 150–180

    Selection Criteria Beyond Temperature

  • Chemical environment: PPS resists acids and hydrocarbons but is attacked by chlorine at high temperature; PEEK resists nearly all chemicals; PEI is susceptible to some ketones and chlorinated solvents.
  • Mechanical load at temperature: PEEK retains 70% of room-temperature tensile strength at 200°C; PPS retains 50%; PEI retains 60% — the load-bearing requirement at operating temperature narrows the selection.
  • Processing requirements: high-temp resins need high melt temperature (320–400°C) and heated mold (130–200°C) — the molder must have equipment rated for these conditions; not all shops can process PEEK or LCP.
  • Moisture sensitivity: most high-temp resins are hygroscopic and require drying to 0.02% moisture or less before molding — wet material causes splay, voids and molecular degradation at processing temperatures.

    • What This Means for Your Quotation

    The material selection starts with the continuous use temperature, chemical environment and mechanical load — not the peak temperature or the most expensive grade. The quotation names the specific resin grade with its RTI, the processing requirements (mold temperature, melt temperature, drying spec) and the per-part cost at the expected volume. When the resin is justified by the application data, the cost is controlled; when the selection defaults to the highest grade, the part costs 5–10× more than necessary.

    Frequently Asked Questions

    Can standard engineering resins handle 150°C?

    Some — glass-filled PA66 handles 140–150°C short-term; PBT with 30% glass handles 130–140°C. For continuous use above 150°C, you move into specialty resins (PPS, PPA, PEI). The RTI of the specific grade — not the resin family — is the selection criterion.

    Does the mold need to be different for high-temp resins?

    Yes — the mold must withstand higher temperatures (heated to 130–200°C) and resist abrasion from glass-filled grades. Mold steel selection matters: S136 or H13 hardened to 48+ HRC for glass-filled PPS or PEEK; standard P20 wears too quickly. The mold design also needs larger gates and runners for the higher viscosity melt.

    How do you validate the resin selection?

    The resin supplier’s datasheet provides RTI, mechanical properties at temperature and chemical resistance data. For critical applications, request aged samples tested after 1,000+ hours at the operating temperature — this confirms long-term performance, not just the short-term datasheet values.

    Key Takeaways

    1. High-temperature resin selection is driven by continuous use temperature (RTI), chemical environment and mechanical load at temperature — not peak temperature or defaulting to the most expensive grade.
    2. Processing requirements are demanding: high melt temperatures (320–400°C), heated molds (130–200°C) and strict drying specs — the molder must have the right equipment.
    3. The quotation should name the specific grade with RTI, processing requirements and per-part cost — so the resin is justified by application data, not assumed.

    Send aCatMould the operating temperature, chemical environment and mechanical load, and the material recommendation names the grade with the lowest cost that meets the requirements — with processing specs and mold steel selection documented, so the resin is justified by data, not by the highest grade on the shelf.

    Sources
    Plastics Technology — high-temperature resin selection
    Solvay — specialty polymer datasheets (PPS, PEEK, PEI)
    Underwriters Laboratories — Relative Thermal Index database

    Sources: Plastics Technology · Plastics Technology Online · Society of Plastics Engineers (SPE) · ThomasNet