Select a high-performance plastic by the requirement that ordinary engineering resins cannot meet. Temperature alone is not enough. Chemical exposure, creep, wear, dimensional stability, flame or smoke, electrical behavior, sterilization, moisture, part geometry, processing and cost can point to different grades.
This decision guide is for engineers and sourcing teams evaluating PEEK, PPS, PEI, LCP and related high-performance injection-molding materials. It does not treat a polymer family as proof of compliance or finished-part performance.
Define the Performance Gap First
Write down the load, duration, temperature cycle, chemicals, humidity, wear mechanism, electrical function, fire requirement, dimensional interface and expected life. Identify what fails with the current material. A measurable gap prevents an expensive resin from being selected simply because it has the highest headline property.
Requirement-to-Material Shortlist
| Dominant requirement | Families often screened | Questions that can change the choice |
|---|---|---|
| High heat plus mechanical retention | PEEK, PEI, PPS and reinforced grades | Continuous versus short exposure, load duration, oxidation and joining |
| Chemical and fluid exposure | PEEK, PPS, selected fluoropolymers or specialty grades | Exact chemical, concentration, stress, temperature and exposure time |
| Thin electrical connector geometry | LCP, PPS and specialty flame-rated grades | Weld lines, tracking, terminal retention, warpage and rating thickness |
| Wear and friction | Bearing-modified PEEK, PPS or other tribological compounds | Counterface, speed, load, lubrication, heat and debris |
| Dimensional stability | PPS, LCP, reinforced PEEK or PEI depending on environment | Flow orientation, moisture, thermal expansion, post-mold change |
PEEK: Broad Capability With a High Processing Burden
PEEK grades may be considered for demanding heat, chemical, wear and mechanical environments. Reinforcement and bearing additives change stiffness, shrinkage, surface and tool wear. Crystallinity and thermal history affect performance, so mold-temperature control and part thickness need attention. PEEK should be justified by the application and exact grade data rather than a general claim that it replaces metal.
PPS: Dimensional and Chemical Performance With Flow and Brittleness Tradeoffs
PPS is often screened for electrical, automotive-fluid and industrial components. Many commercial grades are reinforced. Low melt viscosity can help fill thin features but places demands on shutoffs and flash control. Fiber orientation, weld-line location and brittle failure modes must be reviewed for clips, terminals and press-fit features.
PEI: Amorphous Heat Performance and Optical or Electrical Options
PEI can offer heat, dimensional and electrical performance in an amorphous resin family. Chemical stress cracking, color, moisture preparation and high processing temperature remain part of the decision. Transparent grades do not eliminate the need to control stress, gate location and surface quality.
LCP: Thin-Wall Flow With Strong Directionality
LCP is frequently evaluated for thin electrical and precision components because of its flow behavior and dimensional potential. Its molecular and fiber orientation can produce strongly directional properties and shrinkage. Gate layout, weld lines, wall transitions and connector loads should be modeled and validated with the actual grade.
Do Not Compare Generic Data-Sheet Maxima
Use the same test condition, units, specimen orientation, temperature and moisture state. A property measured on a standard specimen may not transfer directly to a thin molded rib, weld line or fiber-oriented region. Request current technical data and processing guidance from the resin manufacturer, then build a requirement matrix with pass, margin and unknown columns.
Tooling and Machine Readiness
- Confirm machine temperature, pressure, residence and shot-size capability for the grade.
- Review steel, hardness, coatings and gate wear for reinforced compounds.
- Design heating and cooling for the required mold-temperature range and uniformity.
- Provide venting without creating flash-prone shutoffs.
- Plan purge, contamination control and safe material handling.
- Allow service access for gates, vents and wear components.
Illustrative Selection Example
This is a hypothetical screening example. A fluid-control component must retain dimensions under heat and chemical exposure. The team compares one PPS grade and one PEEK grade using the exact fluid, temperature, stress and time. PPS appears lower in material cost, while PEEK provides more margin in one chemical condition. Tooling, cycle, machining, inspection and validation are added to the annual cost model. The result may favor either grade depending on geometry and evidence; the example does not declare a universal winner.
Validation Plan Before Production
Test molded parts from representative cavities and process conditions. Include the failure modes that drove the material change: creep, pressure, chemical exposure, thermal cycling, wear, electrical or fire performance, dimensional stability and assembly. Define conditioning, sample orientation and acceptance criteria. A supplier certificate supports traceability but does not replace part validation.
Questions for the RFQ
Is PEEK generally the best high-temperature plastic?
No. It may be unnecessary, incompatible with a chemical or too expensive for the required margin. PPS, PEI, LCP or another grade may fit the complete requirement better.
Why can the same polymer produce different results?
Reinforcement, additives, molecular structure, lot, moisture, processing, crystallinity, geometry and flow orientation all affect molded performance.
When should moldflow analysis be used?
Use it when gate, filling, pressure, fiber orientation, weld lines, shrinkage or warpage risks cannot be resolved confidently from simpler evidence. The model inputs and assumptions must match the intended grade and process.
Review the full material-selection context and submit the exact service conditions through CKMOLD’s RFQ form. A DFM review can then connect the grade to tooling and validation.