PPS vs PEI: Which Material Is Better for Electrical Insulation Parts?
A direct technical comparison of Polyphenylene Sulfide (PPS) and Polyetherimide (PEI / Ultem) for precision-machined electrical insulators, high-voltage terminals, connectors, and semiconductor components.
Both PPS (Polyphenylene Sulfide) and PEI (Polyetherimide / Ultem) rank among the top-tier dielectric thermoplastics. If your application demands continuous broad-spectrum chemical immersion and superior high-temperature stiffness at minimum raw material cost, PPS wins. If you require higher dielectric strength, optical clarity, tighter unreinforced machining tolerances, and extreme resistance to micro-cracking under mechanical impact, PEI is your optimal choice.
Introduction to PPS and PEI for Electrical Applications
Modern electrical distribution units, power electronics, battery systems, and semiconductor test sockets operate under severe thermodynamic constraints. As operational voltages increase and enclosure footprints shrink, traditional engineering plastics like Nylon, Delrin (POM), and standard Polycarbonate fail due to thermal deformation, moisture-induced arc tracking, or chemical degradation.
In our precision CNC machining facility at PlasticCNCPro, we frequently consult with hardware engineers who are caught between two high-performance thermoplastics: Polyphenylene Sulfide (PPS) and Polyetherimide (PEI, famously known by SABIC's brand Ultem®). Selecting the right polymer involves balancing dielectric breakdown thresholds, mechanical stress, thermal expansion, chemical exposure, and overall machining economics.
What Is PPS Plastic?
Polyphenylene Sulfide (PPS) is a semi-crystalline, high-performance thermoplastic composed of alternating sulfur atoms and para-substituted phenylene rings. This tightly bound, symmetric chemical backbone provides PPS with extraordinary resistance to chemical degradation, superior thermal stability, and intrinsic flame resistance without the need for halogenated flame-retardant additives (achieving UL94 V-0 ratings naturally).
In electrical assemblies, PPS is valued because its electrical insulation characteristics remain practically flat across wide temperature and frequency variations. Furthermore, PPS absorbs virtually zero moisture (<0.05% at 24 hours), meaning parts do not swell or lose their dielectric isolation when operating in high-humidity outdoor switchgear or marine electronics.
What Temperatures Can PPS Plastic Withstand?
When sizing insulating bushings, coil bobbins, or high-current contact carriers, thermal endurance is non-negotiable. PPS displays outstanding thermal metrics:
Because PPS is semi-crystalline, it retains substantial mechanical rigidity above its glass transition point (~85°C), particularly in glass-fiber or mineral-filled variants (such as PPS-GF30 or PPS-GF40), which are standard choices for CNC machined power insulators.
What Is PEI Material?
Polyetherimide (PEI), universally specified under SABIC's brand name Ultem® (predominantly Ultem 1000 unfilled and Ultem 2300 30% glass-reinforced), is an amorphous amber-transparent polyimide polymer. Its repeating units feature rigid aromatic imide rings linked by flexible ether bonds.
Unlike semi-crystalline plastics, PEI's amorphous molecular morphology imparts isotropic mechanical properties, minimal post-machining residual stress deformation, exceptionally high dielectric strength across extreme temperature spans, and superior impact ductility. In semiconductor test sockets, wafer handling, and avionics connectors, PEI is an industry benchmark.
Key Material Properties Comparison: PPS vs PEI
Below is an empirical property summary evaluating electrical-grade unreinforced and 30% glass-reinforced stock shapes commonly used in our CNC turning and milling centers:
| Property | Test Method | PPS (Unfilled / GF30) | PEI / Ultem (1000 / 2300) |
|---|---|---|---|
| Polymer Structure | — | Semi-crystalline | Amorphous |
| Dielectric Strength (1mm) | ASTM D149 | 18 – 21 kV/mm | 25 – 33 kV/mm |
| Dielectric Constant (1 MHz) | ASTM D150 | 3.0 – 3.2 | 3.15 – 3.5 |
| Dissipation Factor (1 MHz) | ASTM D150 | 0.001 – 0.002 | 0.0025 – 0.005 |
| Volume Resistivity | ASTM D257 | 10^16 Ω·cm | 10^16 – 10^17 Ω·cm |
| Continuous Service Temp | UL 746B | 220°C – 240°C | 170°C – 180°C |
| Tensile Strength (Yield) | ASTM D638 | 80 MPa (Unfilled) / 160 MPa (GF30) | 105 MPa (1000) / 170 MPa (2300) |
| Moisture Absorption (24h) | ASTM D570 | 0.02% – 0.05% | 0.25% |
| Chemical Resistance | — | Virtually inert (<200°C) | Sensitive to polar solvents/esters |
Electrical Insulation Performance
When raw dielectric breakdown voltage is the primary design limiter, PEI outperforms PPS. With dielectric strengths exceeding 25–30 kV/mm in thin-wall cross-sections, PEI prevents pinhole breakdown in compact aerospace multi-pin connectors. However, PPS demonstrates a lower dissipation factor (loss tangent) at high frequencies (gigahertz range), making PPS exceptional for high-frequency RF transmission isolators and microwave cavity housings.
Thermal Stability and Heat Resistance
PPS holds the advantage in absolute continuous operating temperature (220°C–240°C vs. 170°C for PEI). If an insulator must reside inside an oil-cooled transformer, alongside an engine exhaust harness, or near power invertor MOSFETs subject to constant 200°C thermal soak, PPS prevents creep and degradation. In contrast, PEI softens significantly once approaching its glass transition temperature (Tg) of 217°C.
Mechanical Strength and Dimensional Stability
Unfilled PEI (Ultem 1000) possesses remarkable tensile yield strength (105 MPa) and ductility, resisting brittle fractures when pins are pressed into machined holes. Unfilled PPS is inherently brittle; dropping an intricate thin-walled unfilled PPS component onto concrete can cause cracking. Therefore, we generally machine PPS from glass-reinforced stock. Furthermore, because PEI is amorphous, its shrinkage is completely isotropic, allowing us to machine parts to tolerances as tight as ±0.01 mm without post-clamping warping.
Chemical Resistance and Environmental Stability
PPS is virtually impervious to almost all industrial chemicals below 200°C, having no known solvent at ambient temperatures. It is unaffected by automotive brake fluids, transmission oils, battery electrolytes, acids, and aggressive cleaning fluids. PEI, while resistant to mineral acids and alcohols, is vulnerable to stress-cracking when exposed to chlorinated solvents, ketones (like acetone), esters, and aromatic hydrocarbons.
PPS vs PEI: Which Performs Better for Electrical Insulation Parts?
The verdict depends entirely on the operating environment of your electrical component:
Choose PEI (Ultem) When:
- Maximum dielectric breakdown strength is needed across compact wall thicknesses.
- Parts require interference-fit press pins or snap latches that require mechanical toughness.
- Optical transparency or visual internal inspection of contacts is beneficial.
- Operating temperatures remain consistently below 170°C.
Choose PPS When:
- The component faces harsh oils, fuels, coolants, or chemical cleaning washdowns.
- Continuous temperatures exceed 180°C up to 240°C.
- Zero moisture absorption is essential to eliminate dimensional swelling and leakage current.
- Raw stock material cost optimization is a major priority for low-to-medium volumes.
Common Applications in Electrical and Electronics Industries
Both plastics serve mission-critical electrical functions across industries we support at PlasticCNCPro:
PPS Typical Components:
Automotive EV battery disconnect housings, high-temperature terminal blocks, electric motor brush holders, pump motor insulators, IGBT power module brackets, switchgear arc chutes, and chemical sensor electrical isolators.
PEI (Ultem) Typical Components:
Semiconductor burn-in test sockets (BiTS), IC chip test nests, high-density avionics circular connectors, microwave guide isolators, fiber optic connector blocks, medical instrument isolation chucks, and aerospace radome circuit supports.
Pros and Cons of PPS for Electrical Insulation
- • Inherent UL94 V-0 flame rating with zero halogen toxicity.
- • Exceptional continuous heat threshold up to 240°C.
- • Near-total chemical immunity to organic and inorganic reagents.
- • Extremely low water uptake ensures stable dielectric constants in humid climates.
- • Generally lower raw material cost than PEI.
- • Unfilled grades suffer from brittleness and notch sensitivity.
- • Glass-filled stock causes accelerated cutting tool wear during CNC milling.
- • Semi-crystalline structure can yield slight anisotropic thermal expansion.
- • Completely opaque; internal contact inspection is not possible.
Pros and Cons of PEI for Electrical Insulation
- • Superior dielectric strength (up to 33 kV/mm).
- • Exceptional mechanical toughness and high tensile modulus.
- • High dimensional predictability during CNC machining (±0.01 mm).
- • Natural amber translucency enables optical verification of internal parts.
- • Exceptional retention of dielectric properties at cryogenic temperatures.
- • Susceptible to environmental stress cracking from ketones, aromatics, and brake cleaners.
- • Lower maximum continuous temperature (170°C vs. 240°C for PPS).
- • Higher moisture absorption rate (0.25%), requiring pre-drying if used in dry-sealed enclosures.
- • Substantially higher material stock cost.
How to Choose Between PPS and PEI for Your Project
When reviewing 2D drawings and specifications, our machining engineering team uses the following 4-point evaluation matrix to help customers decide:
Evaluate Voltage Gradient & Wall Thickness
If your design features miniature walls (<0.8 mm) carrying voltages >5 kV, PEI's higher dielectric strength is vital to eliminate breakdown risks.
Identify Fluid and Solvent Exposure
If the insulator comes into contact with fuels, engine oils, industrial washdown degreasers, or steam, PPS provides chemical longevity where PEI may craze or stress-crack.
Assess Mechanical Fastening Method
If brass pins, threaded helicoils, or interference snap pins are forced into the plastic, PEI handles mechanical shear stresses far better than notch-sensitive PPS.
Budget and Prototyping Quantities
For medium-to-large machined production runs where both thermal and electrical specs are met, PPS typically reduces overall raw stock billet costs by 15% to 30% compared to Ultem 1000.
Frequently Asked Questions
What Are the Key Differences Between PPS and PEI?
The primary differences stem from their polymer physics: PPS is semi-crystalline with exceptional chemical resistance, zero water absorption, and a 240°C continuous thermal ceiling. PEI is an amorphous polymer offering significantly higher dielectric strength (up to 33 kV/mm), amber translucency, superior mechanical toughness, and tighter isotropic machining tolerances, though with reduced chemical resistance against polar solvents.
Which Plastic Has the Highest Melting Point?
PPS has a true crystalline melting point (Tm) of approximately 285°C (545°F). Because PEI is an amorphous polymer, it does not possess a true crystalline melting point; rather, it exhibits a glass transition temperature (Tg) of roughly 217°C (423°F), above which it gradually softens. Therefore, PPS withstands higher peak thermal spikes, such as automated soldering reflow cycles.
Is PPS a Good Electrical Insulator?
Yes, PPS is an outstanding electrical insulator. It offers a high volume resistivity of 10^16 Ω·cm, an ASTM D149 dielectric strength of 18–21 kV/mm, and remarkably low dielectric loss (tan δ ~ 0.001) that remains uniform across frequencies up to 10 GHz. Combined with near-zero moisture absorption and UL94 V-0 flame retardancy, it is widely used in high-voltage industrial and automotive components.
Request a DFM Review & Machining Quote
Send us your 2D drawings, 3D CAD models (STEP, IGES), and application specifications. Our engineering team in Dongguan will review your design for manufacturability, verify PPS vs. PEI suitability, and return an itemized quotation with rapid prototype or production lead times.