PEI Plastic: Properties, ULTEM Grades, Uses and Injection Molding

PEI plastic is used when ordinary engineering plastics no longer provide enough heat resistance, flame performance, electrical insulation, or dimensional stability. It appears in electrical connectors, high-temperature housings, automotive components, aerospace parts, and demanding industrial assemblies.

However, PEI is expensive and less forgiving to process than ABS, PC, or PA. At HingTung, material selection is therefore reviewed around the actual temperature, load, tolerance, environment, and production requirements rather than simply choosing the highest-performance resin available.

What Is PEI Plastic?

What is PEI plastic? PEI stands for polyetherimide. It is an amorphous high-performance thermoplastic with an amber-transparent appearance in many unfilled grades. Compared with common plastic injection molding materials, this PEI plastic material is mainly considered when heat, flame resistance, electrical performance, or dimensional stability becomes critical.

The PEI polymer contains rigid imide groups together with ether linkages. This PEI structure helps combine high-temperature performance with melt processability, allowing polyetherimide plastic to be injection molded, extruded, and formed into other commercial shapes.

Is PEI the Same as ULTEM?

PEI is the generic polymer family. ULTEM™ is SABIC’s well-known commercial PEI material family, so ULTEM plastic is PEI, but PEI from other manufacturers is not ULTEM. Current SABIC grades include unfilled and reinforced versions designed for different mechanical, flow, flame, and compliance requirements.

This distinction is useful when a drawing simply specifies ULTEM PEI or when a supplier quotes an alternative polyetherimide PEI grade. The exact resin grade and its technical data sheet should still be approved before production.

PEI Plastic Properties

PEI belongs to the group of heat-resistant plastics, but generic statements such as “high strength” or “high heat resistance” are not enough for engineering selection. The table below uses unfilled ULTEM 1000 as a representative commercial grade. Actual values vary by grade, filler, thickness, conditioning, and test method.

Property	Representative Value	Engineering Relevance
Glass transition temperature	217°C	Indicates the high-temperature capability of the amorphous polymer
Tensile yield strength	110–115 MPa	Useful for structural and load-bearing parts
Tensile modulus	3.2–3.35 GPa	Indicates relatively high stiffness
HDT at 1.82 MPa	about 190–201°C	Useful when evaluating loaded parts at temperature
Density	1.27 g/cm³	Relatively low compared with metals
Thermal conductivity	0.22 W/m·K	PEI is primarily an insulator, not a heat-spreading material
Mold shrinkage	0.5–0.7%	Important for mold sizing and dimensional prediction
Relative temperature index	170°C	Reference for long-term electrical/mechanical temperature performance

These figures should never replace the selected PEI material data sheet. For example, reinforcement can change stiffness, shrinkage, flow, impact behavior, and dimensional response substantially.

Does PEI Plastic Have a Melting Point?

Searching for the PEI plastic melting point can be misleading. PEI is an amorphous thermoplastic, so it does not have the sharp crystalline melting point found in semi-crystalline materials such as PEEK.

For engineering work, glass transition temperature, heat-deflection temperature, service temperature, and processing temperature are more useful. Representative PEI has a Tg around 217°C, while published continuous-use values for some PEI products are around 170°C.

Advantages and Limitations of PEI

PEI combines several properties that are difficult to achieve together. It offers high heat resistance, good stiffness, electrical insulation, inherent flame resistance in many grades, low smoke behavior, hydrolytic stability, and relatively low dimensional change. These ULTEM properties explain its use in electrical and transportation applications.

The trade-offs are equally important.

Limitation	Why It Matters
High resin cost	PEI is significantly more expensive than standard engineering plastics
High processing temperature	Machines, heaters, molds, and temperature-control equipment must support the process
Moisture sensitivity before molding	Poor drying can reduce processing stability and part quality
Chemical limitations	Certain aggressive solvents and chemical environments can cause stress cracking
Notch sensitivity	Sharp geometry and local stress concentrations need careful design
Filled-grade tooling wear	Glass reinforcement increases abrasion at gates and other wear areas

Why Is PEI Plastic So Expensive?

PEI material price reflects more than the cost of polymer pellets. Specialty resin production, reinforcement, certified grades, relatively lower market volume, and high performance all contribute to resin cost.

Finished-part cost can rise further because PEI requires high-temperature drying and molding, controlled tooling, longer setup, and careful scrap management. This is why PEI should solve a real performance requirement rather than simply replace a cheaper resin that already works.

Common PEI and ULTEM Grades

There is no single “standard PEI” for every application. Grade selection changes the balance between flow, stiffness, dimensional stability, impact performance, color, compliance, and cost.

PEI Type	Example	Main Difference
Unfilled PEI	ULTEM 1000	General balance of heat, strength, electrical performance, and dimensional stability
10% glass-filled	ULTEM 2100	Increased stiffness
20% glass-filled	ULTEM 2200	Higher rigidity and dimensional control
30% glass-filled	ULTEM 2300	High stiffness for structural and precision applications
Specialty grades	Medical, high-flow, conductive or compliance-specific grades	Designed around specific application requirements

The difference can be substantial. SABIC currently lists a tensile modulus of about 3.2 GPa for unfilled ULTEM 1000, while 30% glass-filled ULTEM 2300 reaches about 10.5 GPa. ULTEM 2300 also lists tensile strength at break around 175 MPa.

PEI Plastic Uses

Common PEI plastic uses are concentrated in applications where several requirements occur together. Heat resistance alone does not automatically justify PEI.

Industry	Typical Parts	Why PEI Is Considered
Electrical and electronics	Connectors, insulators, relay parts, high-temperature housings	Heat, dielectric properties, flame performance
Automotive	Under-hood electrical parts, sensors, connectors	Heat and dimensional stability
Aerospace and transportation	Interior components, brackets, electrical parts	Flame, smoke, weight, temperature
Laboratory and healthcare	Instrument components, trays, selected reusable parts	Heat and repeated sterilization capability in suitable grades
Industrial equipment	Insulators, housings, valve or pump components	Heat, stiffness, dimensional stability

Chemical compatibility, compliance, sterilization method, load, and temperature must still be checked against the exact grade. A generic PEI name is not enough for material approval.

PEI Injection Molding

ULTEM injection molding and other PEI molding processes operate at much higher temperatures than standard ABS or PP molding. Drying, residence time, mold heating, venting, gate design, and machine capability therefore become part of material selection, not just production setup.

For reference, SABIC currently publishes the following general conditions for ULTEM 1000. These values are starting guidelines, not universal settings for every PEI resin or part geometry.

Process Parameter	ULTEM 1000 Reference
Drying temperature	150°C
Drying time	4–6 h
Maximum moisture	0.02%
Melt temperature	350–410°C
Mold temperature	135–180°C
Back pressure	0.3–0.7 MPa
Recommended vent depth	0.025–0.076 mm

For filled grades, abrasion becomes another concern. Gate areas, runners, inserts, and wear surfaces should be reviewed together with injection mold tool steel and expected production volume.

HingTung can review material behavior, part geometry, gating, venting, tooling, and trial requirements as part of the DFM and custom injection molding workflow before tooling is released. HingTung’s current service scope includes material selection support, DFM, mold manufacturing, molding, process control, inspection, and repeat production.

Design Considerations for PEI Molded Parts

Good dimensional stability does not mean PEI automatically produces tight-tolerance parts. Geometry, orientation in reinforced grades, gates, mold temperature, cooling, packing, and measurement conditions still affect the result.

Design Area	Practical Consideration
Wall thickness	Keep transitions gradual to reduce filling and cooling imbalance
Corners	Add radii where possible to reduce stress concentration
Ribs and bosses	Avoid unnecessarily thick intersections
Draft	Provide reliable ejection for stiff PEI parts
Glass-filled grades	Consider fiber orientation, anisotropic shrinkage, and tool wear
Critical dimensions	Define functional plastic injection molding tolerances during DFM

PEI vs PEEK vs PSU

Material comparison is more useful than asking which resin is simply “better.” PEI, PEEK, and PSU occupy different performance and cost ranges.

Material	Main Strength	Main Trade-Off
PEI	Heat, flame, electrical performance, stiffness, dimensional stability	Cost, high processing temperature, some chemical limitations
PEEK	Higher long-term temperature capability and excellent performance in harsh environments	Usually higher resin and processing cost
PSU	Good heat and hydrolysis resistance at a lower performance level	Lower continuous temperature and stiffness than PEI in many applications

For example, Ensinger lists continuous-use references of about 170°C for PEI and 160°C for PSU, while its high-performance material data places PEEK substantially higher.

For applications approaching PEI’s limits, our guide to PEEK injection molding explains the additional temperature, chemical, crystallinity, and processing considerations.

FAQs

Can PEI absorb moisture after molding?

Yes. Representative unfilled ULTEM 1000 data lists about 0.25% water absorption after 24 hours at 23°C and higher values at saturation. The effect on the finished part should be evaluated when dimensional or electrical performance is critical.

Can PEI be used outdoors?

Potentially, but outdoor performance depends on the exact grade, color, UV exposure, stress, temperature, and required lifetime. Do not assume every PEI grade has the same weathering performance.

Can PEI parts be machined after injection molding?

Yes. Secondary machining can be used for selected critical features, but the need for machining should be identified early because fixturing, residual stress, tolerance, and cost may affect the production plan.

Can PEI be colored?

Yes, commercial PEI grades can be supplied in natural amber as well as selected transparent or opaque colors. Color availability and compliance should be confirmed for the actual resin grade.

Conclusion

PEI plastic is valuable when a molded part genuinely needs high heat resistance, flame performance, electrical insulation, stiffness, and dimensional stability. It is not automatically the right choice simply because it is a high-performance polymer. Grade, environment, design, processing window, compliance, and total part cost all need to be reviewed together.

If your project is evaluating PEI or another high-performance resin, HingTung can review the drawing, material requirements, tolerances, tooling, and production conditions before mold manufacturing begins.

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