Last updated: 2026-09-05 · 5 min read

PPS vs. PEEK — How Do These Two High-Temperature Engineering Resins Compare for Injection Molded Parts?

PPS: continuous service 220–240°C, melt 300–330°C, resin $8–15/kg. PEEK: continuous 250–260°C, melt 360–400°C, resin $80–120/kg. Performance gap is real but narrow — PEEK handles 20–40°C more heat with better mechanical strength at temperature — while the cost gap is 8–10×. The question is not which resin is better; it is whether your application actually needs PEEK’s extra performance.

Key Facts

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  • Both semi-crystalline, both require high mold temperatures (150–200°C), both demand aggressive drying (150°C for 3–6 hours). Mold and process requirements are similar — part cost difference comes almost entirely from resin price.
  • Glass-filled PPS (GF40) has higher HDT (260°C) than unfilled PEEK (152°C). For many structural applications below 240°C, PPS-GF40 performs as well as PEEK at a fraction of the cost.
  • For a 10 g part at 500K shots/year: total annual cost $117,500 (PPS-GF40) vs. $689,000 (PEEK-GF30). PEEK costs 6× more for 20–40°C more continuous heat.

    • Process parameter — A controllable variable in the injection molding process: melt temperature, injection speed, holding pressure, cooling time, mold temperature. Each parameter affects part quality — deviations cause defects. Parameters are set during T1 and locked for production. The related guide covers adjacent topics.

    What Are the Mechanical and Thermal Differences at Room Temperature and at 200°C?

    Property PPS (unfilled) PPS (GF40) PEEK (unfilled) PEEK (CF30)
    Tensile strength (23°C) 65 MPa 155 MPa 100 MPa 210 MPa
    Flexural modulus (23°C) 4.0 GPa 14 GPa 3.6 GPa 20 GPa
    HDT at 1.8 MPa 260°C 260°C 152°C 315°C
    Continuous use temp 220–240°C 220–240°C 250–260°C 250–260°C
    Water absorption (24h) 0.02% 0.03% 0.10% 0.05%
    UL94 rating (0.8mm) V-0 V-0 V-0 V-0
    Resin cost $8–15/kg $10–18/kg $80–120/kg $100–150/kg

    Glass-filled PPS has a higher HDT (260°C) than unfilled PEEK (152°C) — for many structural applications at 200°C, PPS-GF40 performs as well as PEEK at a fraction of the cost. PEEK’s advantage appears above 240°C and in unfilled grades where toughness and chemical resistance dominate.

    When Should You Choose PPS Over PEEK?

    Choose PPS when: maximum continuous temperature is below 240°C, the part requires dimensional stability in hot water or steam, resin cost must stay below $20/kg, and the chemical environment involves fuels, solvents or automotive fluids. PPS has near-zero water absorption (0.02%) — dimensionally stable in wet environments where PEEK absorbs 5× more moisture.

    Choose PEEK when: continuous temperature exceeds 240°C, the part requires impact resistance at high temperature (PEEK elongation at break 50–100% vs. PPS 2–3%), exposure to strong acids or bases (PEEK resists pH 1–14), or the application requires low smoke and toxic gas emission in fire. PEEK also has inherent biocompatibility for reusable surgical instruments and implant-adjacent components.

    Flash — Thin excess material that escapes between the mold parting line or around ejector pins. Cause: insufficient clamp force, worn parting line, excessive injection pressure, or contaminated mold surface. Flash thickness: 0.02–0.1mm. Requires secondary trimming to remove. The related guide covers adjacent topics.

    PPS: up to 240°C at $8–15/kg. PEEK: up to 260°C at $80–120/kg. GF40 PPS has higher HDT (260°C) than unfilled PEEK (152°C). For a 10 g part at 500K shots/year, annual cost: $117,500 (PPS) vs. $689,000 (PEEK). Choose based on whether the application truly needs PEEK’s performance envelope.

  • Key parameter identified — critical variable confirmed against spec.
  • Tolerance within achievable range — commercial ±0.15mm or tighter as needed.
  • Material matched to application — resin grade selected for end-use environment.
  • Process window validated at T1 — parameters locked after first trial.
  • Inspection method defined — CMM, visual, or functional test specified.

    • Frequently Asked Questions

    Can PPS be used as a drop-in replacement for PEEK in existing molds?

    In some cases — if part geometry is simple and performance requirements at temperature are below 240°C. Shrinkage rates differ (PPS-GF40: 0.2–0.4% vs. PEEK-GF30: 0.3–0.5%), so mold dimensions may need adjustment.

    The melt temperature difference (300°C vs. 380°C) means the same mold can run both resins, but process parameters must be re-optimized. Do not assume the same settings will work — melt viscosity and crystallization behavior differ.

    Is there a mid-range alternative between PPS and PEEK?

    PEI (Polyetherimide, Ultem) and PPA (Polyphthalamide) sit between PPS and PEEK in performance and cost. PEI is amorphous, transparent, continuous use 170°C, resin $25–40/kg. PPA is semi-crystalline, continuous use 200–220°C, resin $15–25/kg.

    If your application needs 200°C performance but not 260°C, PPA may close the gap without the PEEK price tag.

    What are the common failure modes when PPS or PEEK parts are molded incorrectly?

    For PPS, the most common failure is incomplete crystallization — if mold temperature drops below 130°C, PPS does not crystallize fully and the part warps or has poor chemical resistance.

    For PEEK, the most common failure is moisture-induced degradation — if resin is not dried below 0.02% moisture before molding, hydrolysis at 380°C breaks polymer chains and the part has brittle properties. Both failures are invisible until the part is in service.

    Key Takeaways

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  • PPS: up to 240°C at $8–15/kg; PEEK: up to 260°C at $80–120/kg — 6× cost for 20–40°C gain.
  • GF40 PPS HDT (260°C) > unfilled PEEK HDT (152°C) — competitive below 240°C.
  • PEEK advantages: impact at temperature, pH 1–14 resistance, low smoke, biocompatibility.
  • Annual cost for 10g/500K parts: $117K (PPS) vs. $689K (PEEK).

    • The PPS vs.
    PEEK decision should be made during the DFM review, not after the first mold trial. If PPS meets requirements at a fraction of the cost, switching to PEEK after mold build wastes the resin investment.

    Sources: Solvay — Ryton PPS and KetaSpire PEEK Technical Datasheets · Celanese — High-Performance Polymers Data Sheets · Society of Plastics Engineers (SPE) — High-Temperature Resin Papers · Victrex — PEEK Processing and Design Guide · ASTM International — Engineering Resin Test Standards

    — Arthur, Tooling Engineer at aCatMould