This comparison shows how to screen PEEK, PEI and PPS by real service conditions, exact-grade data, molding capability and validation evidence rather than by a single headline temperature.
For a wider first-pass screen that includes additional high-heat polymers and automotive or industrial use conditions, see our high-heat plastics selection guide.
PEEK, PEI and PPS are high-performance injection molding materials, but they are not interchangeable high-temperature labels. Each has a different balance of heat retention, chemical resistance, mechanical load, dimensional behavior, electrical performance, flow, processing difficulty and cost. Material selection should begin with the service environment and finish with production-like molding and validation, not with the highest temperature number on a datasheet.
Related CKMOLD resources: mold design, production injection molding, mold testing and validation.
Do not rank PEEK, PEI and PPS by one “ultimate” property. Compare purchasable grades at the required temperature/time/load, chemicals, wear, electrical and dimensional conditions. Reinforcement and additives can change performance, anisotropy, shrinkage, wear and process requirements.
Now that you have the quick overview, you’re probably wondering about the specifics. How do these materials really stack up against each other in real-world applications? Getting these details right is the key to a successful project.
Use Why Mold Temperature Matters for Different Plastic Materials for the material-dependent role of mold temperature. This article isolates PEEK, PEI and PPS selection for hot environments.
What is the difference between PEI Ultem and PEEK?
PEEK and PEI differ by commercial grade, reinforcement and test condition. Some PEEK grades support demanding thermal, mechanical, wear or chemical service; PEI grades can offer useful heat, electrical, dimensional or transparency performance. Do not release 250°C or 170°C as universal structural service limits—compare long-term property retention at the actual load and duration.
Separate must-have requirements from preferences. This prevents paying for an unused headline property while missing a critical load, chemical, electrical, dimensional or manufacturing condition.
Compare PEEK and PEI on the Actual Requirement
| Requirement | Comparison method |
|---|---|
| Long-term heat/load | Exact-grade property retention or recognized rating at duration, load and thickness |
| Strength and creep | Grade, filler, orientation, weld line, temperature and time |
| Chemicals and wear | Specific media, concentration, stress, counterface, speed and lubrication |
| Sterilization | Exact cleaning/steam/radiation sequence, cycles, aging and finished-part acceptance |
| Cost | Current grade quotations plus drying, machine/tool, cycle, yield, inspection and validation |
No universal 170°C service limit, tensile ranking or 5–10× price relationship applies to all PEEK and PEI grades.
Applications of High-Temperature Plastics
Selected grades of PEEK, PPS, PEI, PSU/PPSU, PI or LCP may retain useful properties above temperatures where commodity plastics are unsuitable. Capability depends on grade, reinforcement, load, duration, chemicals, processing and test method; “above 150°C” is not a universal structural guarantee.
Use in the Aerospace Industry
Selected aerospace components use high-performance polymers to reduce mass, but structural reliability, fuel or fluid exposure, temperature, flame, smoke, toxicity and traceability must be demonstrated to the applicable specification. Polymer substitution does not preserve integrity automatically.
The Car Industry
Selected automotive components use high-performance polymers where exact grades meet location-specific heat, fluids, wear, electrical, flame, dimensional and aging requirements. Replacing metal may reduce mass or combine features, but it does not automatically improve emissions, efficiency or durability.
Electronics and Electrical Industries
Selected high-temperature grades are used in connectors, insulators and other electrical components where their dielectric, heat, dimensional and molding behavior meet the specification. Grade, thickness, aging, moisture and flame or electrical test conditions remain controlling.
In the Healthcare Industry
Reusable healthcare components may require exact-grade evidence after the specified cleaning, sterilization and aging sequence. PEEK, PPSU, PEI and other candidates differ by formulation and device requirement; high-temperature capability or a family name does not establish biocompatibility, implant suitability or repeated-cycle life.
Industrial Applications
Pumps, seals, bearings and valves may use high-performance polymers where a selected grade meets heat, wear and media requirements. Compare load, speed, lubrication, clearance, creep, chemical exposure and maintenance with metal and other polymer options.
High-performance polymers can replace metal in selected designs, but load, creep, wear, chemicals, temperature, fire requirements, tolerances and validation determine whether substitution is appropriate. Sustainability or efficiency benefits require a product-level comparison.
What is the difference between PPS and PEEK plastic?
You may be comparing PPS and PEEK spec sheets and noticing two materials that both claim high-temperature performance. It’s a confusing similarity. Making the wrong choice could cause your parts to warp after being subjected to a particular chemical or not have sufficient raw power to withstand a mechanical application, resulting in costly in-the-field failures. Let’s compare their respective strengths so that you’ll understand exactly how PPS’s stability excels and PEEK’s strength is called upon.
PEEK and PPS performance depends on grade, reinforcement, direction, temperature, media and test method. Some PEEK grades can offer useful toughness or wear; filled PPS grades can offer strong chemical and dimensional performance. Compare the exact datasheets and production-like parts instead of declaring one family stronger or chemically superior.
The choice between these two powerful materials often comes down to the specific environment your part will live in. Is it a battlefield of mechanical stress or a bath of harsh chemicals? Answering that question is the first step. Let’s dig into the details that will help you decide.
Compare PPS and PEEK by Grade and Exposure
| Requirement | What controls the comparison |
|---|---|
| Mechanical and creep | Filler, orientation, weld line, load, duration and temperature |
| Chemical resistance | Exact fluid, concentration, temperature, stress and exposure time |
| Dimensions | Moisture, thermal expansion, shrinkage, anisotropy and molding history |
| Wear | Bearing grade, counterface, pressure-velocity, lubrication and temperature |
| Cost | Current grade, tool/machine, cycle, yield, inspection and lifecycle quotation |
Do not infer that PEEK is always stronger, PPS has no relevant solvents below a fixed temperature, or PPS is always the lower-cost answer.
Is PEEK the strongest plastic?
You’ve heard it too often in the trade: “If it must be strong, use PEEK.” The name beckons so many to summon it in every challenging application. But cost can rapidly drive up your price, and “strongest” isn’t even a correct engineering term. You’ll over-design your part and pay more for performance that you do not did require in the first place. Let’s take a clear definition of what “strongest” really is in the plastic trade and determine whether PEEK even deserves that appellation.
PEEK is not the single strongest plastic. Tensile, compressive, impact, creep, fatigue and wear performance rank differently by grade, reinforcement, orientation, temperature and environment. Compare the property and retention relevant to the part.
When “strongest” appears in a requirement, replace it with the controlling property: tensile, compression, impact, creep, fatigue, wear or retention after heat and chemicals. That definition determines whether a PEEK, PEI, PPS or other grade is relevant.
What Does “Strong” Mean for a Plastic?
“Strength” doesn’t even qualify as a value. It’s an aggregate of many different properties that inform us about what a material will do under stress. For a businessman like the buyer, it’s good to understand them in order to not overpay.
PEEK’s Place in the Hierarchy
Selected PEEK grades retain useful properties at elevated temperature and in certain chemicals, but capability is not a universal 250°C structural guarantee. Use the supplier’s long-term thermal, creep, chemical and mechanical data for the exact grade, load and duration, then validate the final part.
PEEK is evaluated in some aerospace, industrial and medical applications, but selection depends on the exact grade, approved specification, load, environment, manufacturing and validation. Implant service and decades of life cannot be inferred from a family datasheet.
How to Choose and Design for High-Performance Plastics in Injection Molding?
High-performance polymer grades are considered when a commodity resin cannot meet a defined combination of heat/load duration, creep, wear, chemicals, dimensions, electrical or regulatory requirements. Capability is grade- and condition-specific; a family label does not guarantee service above 150°C, chemical resistance or dimensional stability.
When selecting a high-performance plastic to be used in injection molding, one ought to consider the operating conditions of the end product. The first factor is usually the temperature resistance, so that the plastic can bear the necessary working environment. Tensile strength, stiffness, and impact resistance are also mechanical properties that contribute largely. When the parts will be subjected to oils, fuels or cleaning agents, then chemical resistance will be an important factor, but in cases where moving parts are needed, then materials with low wear and friction, such as PEEK or PTFE-filled blends, may be required.
High-performance plastics require grade-specific wall, draft, rib, boss, gate, vent, shrinkage, cooling and ejection design. Filled grades can be anisotropic and abrasive, and shrinkage is not universally lower. Set draft and tolerances from geometry, texture, ejection and supplier/tool data rather than a single 1–2° rule.
What is the temperature range for Ultem PEI?
You’re considering PEI (Ultem) because it’s such a great value proposition, balancing cost and performance, but you’re not so sure about its thermal limitations. If you overestimate this, your parts will soften, warp, or completely fail in service, which can cost you in terms of product recall as well as real damage to your reputation. Let’s get extremely clear about what PEI’s exact temperature range is so that you can work with it without reservation in the correct application.
PEI has multiple commercial grades, so continuous-use temperature, HDT and Tg must be read with their test method, load, thickness and duration. Values such as 170°C continuous use, about 200°C HDT or about 217°C Tg may describe selected data but do not release every ULTEM or PEI part for those conditions.
Understanding the temperature ratings on a data sheet is crucial. They aren’t just numbers; they tell a story about where a material can thrive and where it will fail. Let’s translate these technical terms into practical knowledge you can use.
Understanding Key Thermal Properties
When you look at a material data sheet for PEI, you’ll see a few different temperature values. Here’s what they actually mean for your project.
- Long-term thermal rating: use the exact grade’s recognized rating or long-term property-retention data together with actual load and service duration; do not apply one 170°C value to all PEI.
- Heat deflection temperature: HDT is a short-term standardized deflection result at a stated load and specimen condition. It is grade-specific and is not a continuous structural service limit.
- Glass transition: Tg is a material transition measured by a stated method; use the exact grade value and do not treat it as an allowable loaded-part temperature.
Practical Applications Within PEI’s Temperature Range
Illustrative sterilization scenario — not a CKMOLD customer project. A reusable tray candidate should be compared by exact grade after the specified steam, cleaning, drying and aging cycles, including impact, dimensions, color and assembly. PEI is not automatically lower cost or equivalent to PEEK for every tray.
PEI grades are used in selected automotive electrical components, but fluid, heat, electrical, flame, impact and dimensional performance must be verified at the location and after aging. “Low cost” is quotation- and program-specific.
Compare Purchasable Grades at the Real Exposure
Compare purchasable grades at the real exposure. Record manufacturer/grade, filler/additives, color, data test condition and orientation; continuous/peak temperature and time; load/creep/fatigue; chemicals and sterilization; wear; flame/electrical; CTQs and regulatory evidence.
Ask the molder to confirm dryer, barrel/injection unit, residence/purge, mold temperature, steel/coating, gate, vent, wear and handling capability for that grade. At trial, retain process/lot/cavity records and test production-like parts after the stated environment—not only room-temperature datasheet values.
If the grade drives tool and cell risk, include it in product DFM and material review before steel release.
Primary technical sources checked: Victrex — PEEK Injection Molding Guide (PEEK machine, tool and processing requirements); SABIC — ULTEM Resin Portfolio (commercial PEI grade distinctions and declared properties); Celanese — Fortron PPS Design Manual (PPS grade, filler and processing effects). Apply the cited scope to the exact grade, tool and acceptance plan.
PEEK for Severe Mechanical and Chemical Duty
PEEK is often evaluated for demanding temperature, wear, chemical and mechanical applications. Reinforced grades can improve stiffness and dimensional performance, but fiber orientation, weld lines and processing conditions matter. PEEK’s value should be compared with the actual load, temperature cycles, wear mode and service life rather than assumed from its premium price.
PEI for Heat, Electrical and Dimensional Needs
PEI is commonly considered for heat-resistant, electrically functional, transparent or flame-performance applications in selected grades. It can provide a useful balance of strength and dimensional stability, but moisture, processing temperature, color, surface and stress should be reviewed for the exact design.
PPS for Chemical and Dimensional Stability
PPS is often chosen where chemical resistance, low moisture uptake and dimensional stability are important. Filled grades can be stiff and wear-resistant, while flow, weld-line strength, flash control and abrasive behavior must be considered in the mold and machine plan.
Tooling and Processing Are Part of the Choice
High-temperature materials may require controlled drying, heated barrels, higher mold temperatures, suitable machine pressure, corrosion or wear-resistant details and reliable venting. Gate design, runner balance, cooling, draft and ejection should be developed for the selected grade; a tool designed for a commodity resin may not be ready for a high-temperature grade.
Validate After Real Exposure
Compare creep, impact, chemical, thermal cycling, electrical, wear, dimensional and assembly performance at the actual use condition. Record filler, grade, color, drying, processing history and conditioning. A material that wins a room-temperature comparison can lose after heat, chemicals and mechanical load are combined.
PEEK vs. PEI (Ultem) vs. PPS: Buyer Review Checklist
- Define continuous and peak temperature, load, chemicals, moisture, electrical and service-life needs.
- Compare exact PEEK, PEI and PPS grades, including reinforcement and weld-line behavior.
- Check machine, drying, mold temperature, venting, gate, wear and cooling capability.
- Design for anisotropy, shrinkage, inserts, fasteners, ejection and thermal stress.
- Validate production-like parts after realistic thermal, chemical and mechanical exposure.
FAQ
Is PEEK generally better than PEI or PPS?
No. PEEK may offer advantages in severe wear or chemical applications, while PEI or PPS may provide a better balance of electrical, dimensional, chemical or cost requirements.
Are high-temperature plastics difficult to mold?
They can require controlled drying, high melt and mold temperatures, machine reserve, wear-resistant tooling and a tighter process window than commodity resins.
Conclusion
There is no absolute winner: compare named PEEK, PEI and PPS grades against the same thermal, load, chemical, wear, electrical, dimensional, regulatory and manufacturing requirements. Release the choice only after supplier-data review and production-like validation.