What is Poly-ether-ether-ketone (PEEK) Polymer? Properties, Applications & Performance Guide

PEEK: The High-Performance Thermoplastic Solving Critical Engineering Challenges

Polyether ether ketone (PEEK) is a high-performance thermoplastic that engineers turn to when multiple critical requirements must be met simultaneously—something most materials struggle to achieve. While metals, standard polymers, and composites may excel in one area, PEEK delivers across several, making it the material of choice for complex, high-stakes applications.

PEEK solves three critical material challenges that engineers face when metals, standard polymers, and composites fail:

Extreme temperature resistance: 260°C continuous use temperature enables performance in automotive transmissions, some areas in aerospace engines, and oil and gas downhole applications where alternative polymers soften or degrade
Chemical inertness: Resists acids, bases, organic solvents, and hydrocarbons across wide pressure and temperature ranges - critical for chemical processing, medical sterilisation, aerospace, and energy sector applications
Metal-equivalent strength at 40% weight reduction: Specific strength and stiffness many times that of metals and alloys, enabling lightweighting without performance compromise

For material researchers and design engineers evaluating high-performance polymers for critical applications, this combination explains why PEEK increasingly replaces metals in applications worth millions in lifetime value.

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What is PEEK Polymer? Chemical Structure: Understanding Aromatic Polyketones

In the plastics industry, PEEK is widely viewed as a leading high-performance polymer (HPP). However, the materials of choice in the automotive, aerospace, oil & gas and medical device industries have long been metals. PEEK polymer is fast changing that mind-set.

PEEK or polyetheretherketone, belongs to a family of polymers called "aromatic polyketones" (more accurately "polyaryletherketones" or PAEKs). That means it's built up from the following building blocks:

structure

In 1978 ICI filed their patent on PEEK which was first commercialised as Victrex PEEK polymer in 1981

R&D into PAEKs has its origins in the 1960's but it wasn't until 1978 that ICI (Imperial Chemical Industries) filed their patent on PEEK which was first commercialised as Victrex PEEK polymer in 1981.

"Aromatic", usually meaning distinctive or sweet-smelling, may seem a strange word here, but scientists use it to describe some molecules containing or made from ring-like structures (like the aryl building block above). Small molecules of this type, like toluene & naphthalene, have distinct odours, hence the name. PEEK itself however – like most thermoplastics – is odourless under normal conditions. From a chemical point of view, PEEK is a largely linear, semi-crystalline polymer. Here’s how the building blocks fit together and thus we get Ether Ether Ketone or EEK:

This “repeat unit”, shown in the square brackets above, is replicated many times – on average somewhere between 200-300 times – to make a single PEEK polymer chain. The P comes from the Greek “poly” meaning many, so many EEKs make PEEK. The aryl and ketone groups are fairly rigid and provide stiffness which means good mechanical performance combined with a high melting point. The ether groups provide some degree of flexibility, for toughness, and like the aryl and ketone groups are unreactive, so providing resistance to chemical attack. The regular structure of the repeat unit means that PEEK molecules can partially crystallise, and crystallinity provides a combination of wear, creep, fatigue and chemical resistance – more on this later.

The resulting polymer is widely regarded as one of the highest performing thermoplastics in the world. Compared to metals, PEEK-based materials are very light weight, easily shaped, resistant to corrosion and can have considerably higher specific strength (strength per unit weight).

Molecular Weight Effects on PEEK Properties

When we make PEEK, we use a process which controls the length of the chains, or molecular weight. PEEK with longer chains (high molecular weight or MW) tends to be tougher and more impact-resistant than PEEK with short chains. However, high MW polymers are very viscous when molten which can limit their ability to fill small moulds. Low MW PEEK is less impact-resistant but flows much better in the melt so can make small intricate parts easily.

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**Compare PEEK with PPS and PES properties**

View our compare thermal and mechanical, properties across high-performance polymers.

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260°C

Tests have shown that VICTREX PEEK polymer has a continuous use temperature of 260°C (500°F)

## Why PEEK properties make it essential for demanding applications

PEEK does not offer merely two or three properties that mark it as the polymer of choice when high performance is required; it has a whole variety of them. They include thermal and chemical resistance, combined with long-term mechanical strength in dynamic environments whilst being resistant to burning and being processable by most known thermoplastics processes, as the following paragraphs and tables illustrate.

Property	Value	Test Method
Melting Point (Tm) ⁽¹⁾	343°C (649°F)	ISO 11357-3
Glass Transition Temperature (Tg) ⁽¹⁾	143°C (289°F)	ISO 11357-2
Heat Deflection Temperature ⁽¹⁾	152°C (306°F)	ISO 75-2/Af
Thermal Conductivity ⁽¹⁾	0.29 W/m/K	ISO 22007-4
Coefficient of Thermal Expansion (Below Tg, Average) ⁽¹⁾	55 ppm/°K	ISO 11359-2
Coefficient of Thermal Expansion (Above Tg, Average) ⁽¹⁾	140 ppm/°K	ISO 11359-2

Thermal Properties of PEEK

Source 1 VICTREX^TM PEEK POLYMER 450^TM

Thermal Performance: 260℃ Continuous Use Temperature

Tests have shown that VICTREX PEEK polymer has a continuous use temperature of260°C (500°F). This can make it suitable for use in a wide range of thermally aggressive environments, such as those found in the process industries, in the oil and gas sector and inside the engines and transmissions of millions of vehicles. PEEK is able to tolerate friction and resist wear in dynamic applications like thrust washers and seal rings.

Chemical Resistance: Performance in Aggressive Environments

Chemical Group	Resistance
Hydrocarbons (Aliphatic, Aromatic) ⁽¹⁾	Excellent
Organic Solvents (Alcohols, Aldehydes, Ketones, Ethers) ⁽¹⁾	Excellent
Acids (Hydrochloric, Phosphoric) ⁽¹⁾	Excellent
Strong Bases (NaOH, KOH) ⁽¹⁾	Excellent

Chemical properties of PEEK

Source 1 VICTREX PEEK Chemical Resistance Brochure

PEEK is able to resist the damage that can be inflicted in chemically aggressive operational environments, such as downhole in wells in the oil & gas industry, in gears in machinery & automotive applications. It can resist jet fuel, hydraulic fluids, de-icers and insecticides used in the aerospace industry. This holds true over wide ranges of pressure, temperature and time.

Mechanical Strength: Load-bearing performance across Temperature Ranges

Property	Value	Test Method
Tensile Strength (23°C) ⁽¹⁾	78 - 330 MPa	ISO 527
Flexural Strength (23°C) ⁽¹⁾	125 - 480 MPa	ISO 178
Flexural Modulus (23°C) ⁽²⁾	3.2 - 37 GPa	ISO 178
Compressive Strength (23°C) ⁽¹⁾	105 - 310 MPa	ISO 604
Izod Impact Strength (Notched, 23°C) ⁽¹⁾	3.5 - 11 kJ/m²	IISO 180/A

Mechanical Properties of PEEK

Source 1 https://www.victrex.com/-/media/downloads/technical-guides/victrex-product-guide-victrex-peek-properties-en-09-2018.pdf

Creep and Fatigue Resistance for Long-Term Durability

PEEK demonstrates excellent strength and stiffness over a wide temperature range. PEEK-based carbon fibre composites have specific strength many times that of metals and alloys. "Creep" refers to a material becoming permanently deformed over an extended period of time when under constant applied stress. “Fatigue” refers to the brittle failure of a material under a repeated cyclic loading. PEEK has both high creep and fatigue resistance thanks to its semi-crystalline structure and has been shown to be more durable than many other polymers and some metals over a long and useful lifetime.

Flammability Performance: Fire, Smoke Toxicity

PEEK has excellent flammability performance. It resists autoignition up to almost 600°C. When it can be made to burn at very high temperatures, it will not support combustion and it emits little smoke. This is one reason why PEEK is widely used in commercial aircraft.

Processing Versatility: Extrusion to Injection Moulding

The PEEK molecule is very stable, so the polymer can be re-melted and reprocessed again and again with minimal change to its properties. This helps its environmental footprint and can ensure that waste material from manufacturing processes can be mechanically recycled.

As a thermoplastic PEEK can be processed using conventional thermoplastic processing equipment for injection and compression moulding as well as extrusion. It is very versatile and increasingly used for improved part performance, durability, weight saving and overall reduced lifetime system cost. No wonder it's replacing metals and alloys!

Across many industries and critical environments, material experts, part designers and purchasers have to decide whether PEEK is the material of choice to enable advances in performance, weight reduction, energy consumption, assembly time, cost savings or stick to traditional metals and alloys.

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PEEK vs Other High-Performance Polymers: performance Comparison

When compared to other high-heat polymers such as PPS (Polyphenylene Sulfide), and PES (Polyethersulfone), PEEK stands out due to its exceptional balance of heat, wear and chemical resistance and mechanical properties. PEEK's continuous use temperature (Relative Thermal Index), according to UL 746B, of up to 260°C is notably higher than PPS (approximately 240°C) and PES (approximately 180°C), making it suitable for applications that require sustained performance in extreme temperatures. In contrast to PPS, which can soften at lower temperatures, PEEK retains its mechanical integrity even under high thermal stress. In terms of mechanical strength, PEEK offers significantly higher tensile strength compared to both PPS and PES. While PPS is known for its chemical resistance and ease of processing, it lacks the toughness and strength of PEEK, which is critical in applications requiring durable and load-bearing components. PEEK's excellent wear resistance and low friction also give it an advantage over PES, which tends to exhibit inferior wear performance in high-stress environments.

PEEK: Enabling Tomorrow’s Engineering Challenges

PEEK represents more than just a high-performance polymer - it's a material that continues to push the boundaries of what's possible in engineering. Its versatility, strength, and resilience have made it essential in solving some of the toughest challenges across many industries. So it's not just about what PEEK can do today but what it will enable in the future as technologies evolve and demands become more rigorous. If you're looking for a material that offers superb durability, heat resistance, and chemical stability, PEEK might be the answer you've been searching for. To learn more about how PEEK can benefit your specific project or application, we encourage you to Contact Us to learn more.

Frequently asked questions about PEEK

What is PEEK (poly-ether-ether-ketone) used for?

PEEK serves critical applications where metals and standard polymers do not meet multiple key engineering requirements. Primary uses include:

Aerospace: Engine components, structural parts, cable insulation - requires strength, wear, meet smoke, fire, toxicity quality standards, weight-reduction.
Automotive: Transmission components, thrust washers, seal rings - demands reliability, wear properties, performance in high temperatures, chemical resistance.
Oil & Gas: Downhole components, seals, bearings - needs chemical resistance, performance under pressure, extreme temperature performance, reliability.
Medical: Surgical instruments, implantable devices, sterilisation trays - requires biocompatibility, repeated autoclave sterilisation, mechanical performance.
Industrial: Chemical processing equipment, semiconductor components, electrical connectors - leverages chemical inertness and dimensional stability.

How does PEEK compare to metal?

PEEK offers several advantages over metals for demanding applications:

Performance advantages:

Continuous use temperature 260°C matches many metal applications
Specific strength (strength per unit weight) often exceeds metals
Complete chemical inertness (no corrosion vs metal oxidation/degradation)
Excellent wear resistance in dynamic applications
Electrical insulation properties (vs metal conductivity) (Note, carbon fibre filled PAEKs – both as compounds and composites – are conductive, and VICTREX ESD 101 is partially conductive.

Practical advantages:

40-50% weight reduction vs metal equivalents
Complex geometries via injection moulding (vs machining limitations)
Lower assembly costs (snap fits, welded joints vs fasteners)
Reduced maintenance (no corrosion protection required)

Trade-offs:

Higher material cost per kg (offset by part weight reduction and lifecycle savings)
Lower absolute strength than some metals (but higher specific strength)
Processing temperature requirements (360-400°C vs metal forming)

What temperature can PEEK withstand?

PEEK demonstrates exceptional thermal performance:

Continuous use temperature: 260°C (500°F) - validated by measurement according to UL 746B, and used across millions of component hours in automotive and aerospace applications
Melting point: 343°C (649°F) - maintains solid structure well above operating temperatures
Glass transition temperature: 143°C (289°F) - retains mechanical properties above this transition
Short-term excursions: Can tolerate brief exposure to 300°C+ without permanent degradation

This thermal capability significantly exceeds alternative high-performance polymers:

PPS: 240°C continuous use (20°C lower than PEEK)
PES: 180°C continuous use (80°C lower than PEEK)

Is PEEK better than PPS?

PEEK and PPS serve different application requirements:

Choose PEEK when:

Continuous operation greater than 240°C required
Maximum wear resistance needed (dynamic applications)
Highest mechanical strength critical
Specification justifies premium cost for performance advantage

Choose PPS when:

Operating temperature less than 240°C
Cost sensitivity important
Processing ease prioritised (PPS flows more easily)

Performance comparison:

PEEK offers 20°C higher continuous use temperature (260°C vs 240°C)
PEEK provides superior wear resistance and higher tensile strength
PPS costs approximately 30% less than PEEK
PPS processes more easily with shorter cycle times

Real-world guidance: If your application operates at 230-240°C, experiences aggressive chemicals, or requires dynamic wear resistance, PEEK's performance premium typically justifies the cost through extended component life and reduced maintenance. For applications less than 230°C without extreme wear requirements, PPS often provides excellent cost-effective performance.

How much does PEEK cost?

PEEK material pricing reflects its high-performance capabilities:

Material cost considerations:

PEEK costs significantly more than standard engineering polymers PPS, (nylon, acetal) and alternative metal materials e.g. aluminium, steel, titanium.
Price varies by grade: unfilled, glass-filled, carbon-filled grades have different costs.

Design efficiency and waste reduction advantages

Transitioning from metal to PEEK enables component redesign to improve component performance and reduce material usage.
Metal machining can waste up to 80% of material; injection moulding typically generates less than 5–10% waste.
PEEK is sold by weight but used by volume in moulding applications.
Its low density (½ that of aluminium, ⅙ that of steel) means less material is needed for the same part.
PAEKs are compatible with additive manufacturing, further reducing waste.

Curious how High-performing polymers compare to metals? Read our blog PEEK versus Metals.

Lifecycle cost advantages:

40-50% weight reduction vs metals reduces material usage
Component consolidation via complex moulding reduces assembly costs
Extended service life (2-4x vs alternative polymers) reduces replacement frequency
Maintenance reduction (no corrosion, superior wear resistance) lowers total cost of ownership
Reduced downtime in critical applications provides operational cost savings

Cost justification framework: Material researchers and procurement teams typically accept PEEK's premium through:

Application criticality (failure costs exceed material cost premium)
Lifecycle analysis (2-3 year payback through extended service life)
Performance requirements (no alternative polymer meets specifications)
System-level savings (weight reduction, part consolidation, assembly simplification)