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.

What PEEK Does Best

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 where other materials have long since given up.

The chemical resistance story is equally impressive. PEEK resists nearly every chemical at elevated temperatures, including acids, bases, hydrocarbons, and solvents. Only concentrated sulfuric acid and some halogenated compounds affect it, making it the go-to choice when chemical exposure is severe or the exact process fluids aren’t fully characterized.

For applications involving sliding contact or bearing surfaces, unfilled PEEK offers good wear characteristics on its own. Carbon and PTFE-filled grades take this further, providing exceptional bearing performance at high temperatures where other bearing plastics have already failed. PEEK also withstands steam sterilization and hot water exposure indefinitely, which is critical for medical and food processing applications where hydrolysis destroys other materials. The material carries a V-0 flame rating without additives and generates low smoke—inherent properties that simplify regulatory compliance.

Where PEEK Falls Short

The elephant in the room is cost. PEEK runs 5-10x more expensive than PPS or PEI in raw material form, and for large components, this difference becomes substantial. The material can also be brittle under impact, particularly in unfilled grades, so designs must avoid stress concentrations. Processing requires high temperatures and careful technique for both molding and machining.

Typical Applications

PEEK finds its way into oil and gas downhole tools, semiconductor wafer handling equipment, chemical processing machinery, high-performance bearings and seals, wire insulation for extreme environments, and food processing machinery components.

---

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.

What PPS Does Best

The cost equation is PPS’s strongest selling point. At 70-80% less than PEEK, PPS often hits the sweet spot for cost-sensitive applications with serious temperature requirements. You get most of the performance without the premium price tag.

Chemical resistance runs deep with PPS. The material resists most solvents, acids, and bases at elevated temperatures, and no known solvent dissolves PPS below 392°F. Dimensional stability is another strength—low moisture absorption and excellent creep resistance mean PPS maintains dimensions better than many high-temperature alternatives over long service periods.

Like PEEK, PPS carries a V-0 flame rating without additives. On the manufacturing side, PPS is easier to mold than PEEK, with lower processing temperatures and faster cycles that reduce part costs beyond the raw material savings.

Where PPS Falls Short

Brittleness is PPS’s Achilles’ heel. The material is notably brittle, especially in unfilled grades, and impact resistance is poor. Glass-filled grades improve stiffness but remain brittle—if your application involves impact loading, look elsewhere.

The 425°F continuous temperature limit is adequate for many applications but falls short of PEEK’s 480°F capability, and the gap widens for short-term excursions. Most PPS is sold in glass or mineral-filled grades because unfilled PPS is too brittle for practical use. The material can also oxidize over time when operating in air near its temperature limits; PEEK handles oxidizing environments at high temperature more gracefully.

Typical Applications

PPS shows up in automotive under-hood components, electrical connectors and sockets, pump impellers and housings, chemical processing equipment, industrial bearing cages, and cookware handles.

---

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.

What PEI Does Best

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

The material’s high glass transition temperature of 419°F means it maintains stiffness at temperatures where PPS softens significantly. For structural applications requiring rigidity at 300°F and above, PEI excels despite its lower maximum continuous service temperature. This apparent contradiction makes sense when you consider that different applications fail in different ways.

PEI withstands repeated steam cleaning and chemical cycling, making it suitable for food processing and industrial cleaning applications that see aggressive sanitation protocols. Excellent dielectric strength maintained at elevated temperatures makes it a favorite for electrical and electronic applications. Regulatory approvals—FDA, USP Class VI, NSF, and aircraft interior certifications—are readily available.

Where PEI Falls Short

Chemical sensitivity is PEI’s weak point. It’s attacked by chlorinated solvents, ketones, and strong bases, making its chemical resistance notably inferior to PEEK and PPS. The 340°F continuous temperature limit is the lowest of the three, eliminating PEI from the highest-temperature applications.

Like PEEK, PEI can be brittle at stress concentrations. Glass-filled grades improve strength but sacrifice the transparency that makes PEI unique in the first place. The material also absorbs more moisture than PEEK or PPS, affecting dimensions and properties in humid environments.

Typical Applications

PEI finds use in electrical insulators and connectors, food service equipment, analytical instrument components, high-temperature sight glasses, industrial equipment housings, and conveyor components.

---

How to Choose Between Them

Selecting among these three materials comes down to understanding which properties matter most for your application.

PEEK makes sense when you need maximum temperature capability above 425°F, when chemical exposure is severe or not fully characterized, when wear resistance at high temperature is critical, when steam or hot water exposure is part of the service environment, or when the highest mechanical properties justify the premium cost.

PPS is the right call when temperature requirements stay below 425°F, when cost is a significant factor, when chemical resistance is needed (excluding strong bases), when dimensional stability is critical, and when brittleness is acceptable because impact loading isn’t a concern.

PEI earns its place when transparency is required, when stiffness at temperature matters more than absolute maximum temperature, when sterilization compatibility is needed, when chemical exposure is limited to compatible substances, or when electrical properties at temperature are important.

Glass-Filled Grades

All three materials are commonly used in glass-filled grades, typically with 30% glass fiber content. Glass filling dramatically improves stiffness and heat deflection but reduces toughness and eliminates transparency in PEI.

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

Cost Perspective

Rough relative costs for unfilled rod stock in 2” diameter tell the story clearly:

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. It generates long stringy chips that need management, and stress relief through annealing is sometimes worthwhile for precision parts.

PPS produces brittle chips that clear easily and requires lower cutting forces. Watch for chipping at edges and sharp corners—the material’s brittleness shows up during machining too.

PEI behaves similarly to PEEK during machining. Transparent grades can be polished for optical applications, opening up possibilities that the other two materials can’t match.

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.