High-Temperature Plastics Compared: PEEK vs PPS vs PEI

When standard engineering plastics fail—when temperatures exceed 300°F and the application still demands plastic’s weight, corrosion resistance, or electrical properties—three materials dominate: PEEK, PPS, and PEI.

All three handle temperatures that would destroy nylon, acetal, or polycarbonate. But they’re not interchangeable. Each has distinct strengths, weaknesses, and cost profiles. Selecting the wrong one wastes money; selecting the right one enables designs impossible with other materials.

Temperature Capabilities at a Glance

Property	PEEK	PPS	PEI (Ultem)
Continuous Service	480°F (250°C)	425°F (220°C)	340°F (170°C)
Peak/Short-Term	570°F (300°C)	500°F (260°C)	400°F (200°C)
Glass Transition (Tg)	289°F (143°C)	185°F (85°C)	419°F (215°C)
Heat Deflection (264 psi)	320°F (160°C)	275°F (135°C)	392°F (200°C)

Note the apparent contradiction: PEI has lower continuous service temperature but higher heat deflection and glass transition than PPS. This reflects different failure modes—PEI maintains stiffness better but degrades chemically at lower temperatures than PPS.

PEEK: The Premium Choice

PEEK (Polyetheretherketone) represents the pinnacle of thermoplastic performance. When engineers say “we need the best high-temp plastic,” PEEK is usually what they mean.

Strengths

Mechanical properties retained at temperature PEEK maintains significant strength and stiffness at temperatures that reduce other plastics to soft, deformable masses. At 300°F, PEEK retains roughly 50% of room-temperature strength—enough for demanding structural applications.

Exceptional chemical resistance PEEK resists nearly every chemical at elevated temperatures: acids, bases, hydrocarbons, and solvents. Only concentrated sulfuric acid and some halogenated compounds affect it.

Wear and friction performance Unfilled PEEK offers good wear characteristics; carbon and PTFE-filled grades provide exceptional bearing performance at high temperatures where other bearing plastics fail.

Hydrolysis resistance PEEK withstands steam sterilization and hot water exposure indefinitely—critical for medical and food processing applications.

Inherent flame resistance V-0 rated without flame retardant additives. Low smoke generation. Approved for aircraft interiors.

Limitations

Cost PEEK costs 5-10x more than PPS or PEI in raw material form. For large components, this difference is substantial.

Notch sensitivity PEEK can be brittle under impact, particularly in unfilled grades. Design must avoid stress concentrations.

Processing difficulty PEEK requires high processing temperatures and careful technique for molding or machining.

Typical Applications

• Aerospace structural components
• Oil and gas downhole tools
• Semiconductor wafer handling
• Medical implants and surgical instruments
• High-performance bearings and seals
• Wire insulation for extreme environments

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PPS: The Cost-Effective Performer

PPS (Polyphenylene Sulfide) offers impressive high-temperature performance at a fraction of PEEK’s cost. It’s often the practical choice when PEEK’s premium properties aren’t fully required.

Strengths

Cost efficiency PPS typically costs 70-80% less than PEEK. For cost-sensitive applications with high-temperature requirements, PPS often hits the sweet spot.

Chemical resistance PPS resists most solvents, acids, and bases at elevated temperatures. No known solvent dissolves PPS below 392°F.

Dimensional stability Low moisture absorption and excellent creep resistance. PPS maintains dimensions better than many high-temp alternatives.

Inherent flame resistance V-0 rated without additives, similar to PEEK.

Processability Easier to mold than PEEK, with lower processing temperatures and faster cycles.

Limitations

Brittleness PPS is notably brittle, especially unfilled grades. Impact resistance is poor. Glass-filled grades improve stiffness but remain brittle.

Lower temperature ceiling The 425°F continuous limit is adequate for many applications but falls short of PEEK’s 480°F capability. The gap widens for short-term excursions.

Limited unfilled availability Most PPS is sold in glass or mineral-filled grades. Unfilled PPS is brittle and rarely specified.

Oxidation at temperature In air at temperatures approaching limits, PPS can oxidize over time. PEEK is more stable in oxidizing environments at high temperature.

Typical Applications

• Automotive under-hood components
• Electrical connectors and sockets
• Pump components (impellers, housings)
• Chemical processing equipment
• Industrial bearing cages
• Cookware handles

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PEI (Ultem): The Transparent Option

PEI (Polyetherimide), known by the trade name Ultem, occupies a unique position: it’s the only high-temperature plastic available in transparent grades, and it offers the highest heat deflection temperature of the three.

Strengths

Optical clarity Ultem 1000 (unfilled) offers amber transparency. For applications requiring high-temperature visibility—sight glasses, lighting components, medical devices—PEI is often the only option.

Stiffness retention at temperature PEI’s high glass transition temperature (419°F) means it maintains stiffness at temperatures where PPS softens significantly. For structural applications requiring rigidity at 300°F+, PEI excels.

Sterilization compatibility PEI withstands steam sterilization, gamma radiation, and EtO sterilization. This combination makes it essential for reusable medical devices.

Electrical properties Excellent dielectric strength maintained at elevated temperatures. Widely used in electrical/electronic applications.

Regulatory approvals FDA, USP Class VI, NSF, and aircraft interior certifications available.

Limitations

Chemical sensitivity PEI’s weak point. It’s attacked by chlorinated solvents, ketones, and strong bases. Chemical resistance is notably inferior to PEEK and PPS.

Lower continuous temperature The 340°F continuous limit is the lowest of the three, limiting applications in the highest temperature environments.

Notch sensitivity Like PEEK, PEI can be brittle at stress concentrations. Glass-filled grades improve strength but sacrifice transparency.

Moisture absorption PEI absorbs more moisture than PEEK or PPS, affecting dimensions and properties in humid environments.

Typical Applications

• Medical device housings
• Aircraft interior components
• Electrical insulators and connectors
• Food service equipment
• Analytical instrument components
• High-temperature sight glasses

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Selection Matrix

Choose PEEK When:

• Maximum temperature capability is required (>425°F)
• Chemical exposure is severe or unknown
• Wear resistance at high temperature is critical
• Steam, hot water, or hydrolysis exposure
• Highest mechanical properties justify premium cost

Choose PPS When:

• Temperature requirements are below 425°F
• Cost is a significant factor
• Chemical resistance is needed (not including strong bases)
• Dimensional stability is critical
• Brittleness is acceptable (no impact loading)

Choose PEI When:

• Transparency is required
• Stiffness at temperature is critical (despite lower max temp)
• Sterilization compatibility is needed
• Chemical exposure is limited to compatible substances
• Electrical properties at temperature are important

Glass-Filled Grades

All three materials are commonly used in glass-filled grades (typically 30% glass fiber):

Property	PEEK 30% GF	PPS 30% GF	PEI 30% GF
Tensile Strength	24,000 psi	20,000 psi	23,000 psi
Flexural Modulus	1,500,000 psi	1,700,000 psi	1,300,000 psi
Heat Deflection	572°F	500°F	410°F

Glass filling dramatically improves stiffness and heat deflection but reduces toughness and eliminates transparency (in PEI).

Cost Perspective

Rough relative costs (unfilled rod stock, 2” diameter):

Material	Relative Cost
PPS	1.0x (baseline)
PEI	1.2-1.5x
PEEK	4-6x

For many applications, PPS or PEI provides 90% of PEEK’s capability at 20-30% of the cost. The engineering question is whether that last 10% of performance justifies the premium.

Machining Considerations

All three machine readily, but with different characteristics:

PEEK: Machines well but requires sharp tools and controlled feeds. Generates long stringy chips. Can be stress-relieved by annealing.

PPS: Brittle chips that clear easily. Lower cutting forces. Watch for chipping at edges.

PEI: Similar to PEEK machining. Transparent grades can be polished for optical applications.

Working With NextGen Components

We stock PEEK, PPS, and PEI in various forms and grades. Our team can help evaluate which material best fits your temperature, chemical, and mechanical requirements—finding the optimal balance between performance and cost.

Need help selecting a high-temperature plastic? Contact us with your application parameters.