A Comprehensive Guide to High-Performance Polymers and Materials

Most plastics soften or degrade at temperatures that a soldering operation, an engine bay or a steam steriliser reaches routinely. High-performance polymers are the families chosen to keep working under that kind of heat, chemical exposure and load, often for years. This guide explains what earns a polymer the label, how the main types differ, and what the trade-offs look like when you have to choose one.

One caution applies throughout: property values belong to specific grades measured by specific test methods. There is no single number for "PEEK" or "polyimide". Where this article gives a value, it names the grade and the source.

What makes a polymer "high-performance"?

No single standard defines the term. In practice, engineers use it for polymers that combine three things: they retain useful mechanical and electrical properties at temperatures where commodity and most engineering plastics do not; they tolerate demanding chemical, steam or radiation environments; and many are inherently flame-resistant.

Chemistry explains much of this. The high-performance families are built largely from aromatic rings joined by stable linkages such as ethers, ketones, sulfones, sulfides and imides, which restrict chain motion and resist thermal breakdown. The everyday polymers compared in our look at straw materials are chosen for very different reasons.

The image at the top of this article shows two repeat units that make the idea concrete. PEEK links benzene rings through two ether oxygens and a ketone. The polyimide made from pyromellitic dianhydride (PMDA) and 4,4′-oxydianiline (ODA), the textbook aromatic polyimide, fuses aromatic rings into flat imide units.

How thermal endurance is measured: the UL Relative Thermal Index

Short-term heat resistance and long-term heat resistance are different things. A polymer can survive a brief excursion to a high temperature and still age steadily if it is held somewhat lower for months.

The most widely quoted long-term measure for electrical and electronic products is the Relative Thermal Index (RTI), assessed under UL 746B. UL Prospector describes RTI as the maximum service temperature at which specific properties are not unacceptably compromised.⁸ The testing laboratory PTLI describes a thermal index as the temperature below which a material retains sufficient properties, typically 50% of the original value, with a control material of proven field performance used to support the analysis.⁹

RTI comes in three forms: electrical, mechanical with impact, and mechanical without impact.⁸ A single grade can carry different values for each. Victrex, for example, lists PEEK 450G at 260 °C (electrical), 240 °C (mechanical strength) and 180 °C (impact).¹

Tg and Tm: the two temperatures that matter

The glass transition temperature (Tg) is where the amorphous (disordered) regions of a polymer change from glassy to rubbery, and modulus falls substantially through that transition. The melting temperature (Tm) is where crystalline regions melt; only polymers with crystalline regions have one.

That difference produces two broad behaviours:

• Amorphous polymers have a Tg but no crystalline melting point. For them, Tg is an important design boundary because stiffness drops sharply through it, but it is not by itself a universal service-temperature limit. SABIC describes its ULTEM polyetherimide (PEI) resins as amorphous,³ and Syensqo describes its Radel polyphenylsulfone (PPSU) resins as amorphous and transparent.⁵
• Semicrystalline polymers have both. Their crystalline domains can allow them to retain more stiffness above Tg than comparable amorphous polymers, but usable service temperature still depends strongly on load, grade, crystallinity, time and test method. Syensqo describes polyphenylene sulfide (PPS) as semicrystalline.⁴

Two grades show why no single temperature tells the whole story. Victrex PEEK 450G (semicrystalline) has a Tg onset of 143 °C and a heat deflection temperature of 152 °C under a 1.8 MPa load, yet a mechanical-strength RTI of 240 °C.¹ SABIC ULTEM 1000 (amorphous PEI) has a higher Tg of 217 °C and a heat deflection temperature of 192 °C at 1.8 MPa, but an RTI of 170 °C.³ Short-term stiffness under load and long-term thermal ageing measure different things, and neither number alone predicts how a given part will perform.

The main families of high-performance polymers

Polyaryletherketones (PAEK): PEEK and PEKK

PAEKs are semicrystalline polymers of aromatic rings linked by ether and ketone groups, and PEEK is the best known. Victrex's PEEK 450G data sheet lists a melting temperature of 343 °C and a tensile yield stress of 98 MPa at 23 °C (ISO 527).¹ PAEK materials are used in aerospace and biomedical applications.¹⁰ PEKK carries a higher proportion of ketone linkages; printed PEKK can come out with very little crystallinity and may need annealing (see below).^10,11

Polyimides (PI) and polyetherimide (PEI)

Polyimides contain the imide ring in their backbone, and some polyimide films do not melt at all. The Kapton HN data sheet lists the melting point as "None", a second-order transition between 360 and 410 °C, and use from −269 °C up to 400 °C. It gives a tensile strength of 231 MPa at 23 °C (ASTM D882) for the film.² That stability makes polyimide film useful as high-temperature electrical insulation, and it is also what makes polyimides hard to shape.

Polyetherimide adds ether linkages so the polymer can be melt-processed. SABIC's ULTEM 1000 data sheet lists a Tg of 217 °C, a tensile yield stress of 110 MPa (ISO 527), a limiting oxygen index of 47%, and UL 94 V-0 at 0.75 mm or thicker.³

Polyphenylene sulfide (PPS)

PPS is a semicrystalline polymer of benzene rings joined by sulfur atoms. Syensqo gives a crystalline melting point of about 285 °C for its Ryton PPS and reports UL thermal indices of up to 240 °C across Ryton grades. It also states that most Ryton compounds reach UL 94 V-0 without flame-retardant additives, and highlights chemical resistance, saying Ryton PPS has no known organic solvent below 200 °C.⁴ Many PPS grades are filled compounds, so check the exact grade.

Sulfone polymers: PSU, PESU and PPSU

The sulfones link aromatic rings through sulfone and ether groups. Polysulfone (PSU), polyethersulfone (PESU) and polyphenylsulfone (PPSU) differ in backbone structure, and so in heat and impact performance. Syensqo describes its Radel PPSU resins as amorphous, transparent and tough, with strong resistance to hydrolysis in hot water and steam, and says they remain transparent at service temperatures as high as 204 °C.⁵ It also states that Radel PPSU tolerates more than 1,000 sterilisation cycles with minimal property loss, and lists healthcare, plumbing, food service and aircraft among its uses.⁵

Aramids

Aramids are fully aromatic polyamides, usually spun into fibres rather than moulded. Kevlar, a para-aramid, is now part of Arclin, which completed its acquisition of the DuPont aramids business in 2026. Arclin describes Kevlar as a heat-resistant, lightweight synthetic fibre with high tensile strength.⁶ Aramids serve mainly as reinforcement and protective fibres rather than moulding resins.

Fluoropolymers

Fluoropolymers such as PTFE replace the hydrogen on a carbon backbone with fluorine. Chemours' current product information for its Teflon PTFE resins lists a second melting peak of 327 ± 10 °C for its granular and fine-powder grades, and a continuous-use temperature of 260 °C for its PTFE dispersions. It describes products made from the resins as highly resistant to high temperature, chemical attack, corrosion and stress cracking.⁷ Chemours designs its granular grades for compression moulding and its fine-powder grades for extrusion at medium to high reduction ratios followed by sintering.⁷ Fluoropolymers are also the family most exposed to regulatory change (see below).

Liquid crystal polymers (LCPs) and polyphthalamides (PPAs) also appear on many selection shortlists but are outside the scope of this guide.

Representative grades compared

The table lists published values for specific commercial materials. It shows how the families differ, not how every grade behaves. Test methods and specimen forms vary (film, moulded bar, resin), so values in different rows are not directly comparable.

Where they are used

• Aerospace and transport: structural and interior parts and composite matrices, where weight and flame performance matter.^10,12
• Electronics and electrical: polyimide film where insulation must survive high temperatures;² PPS and PEI parts in electrical and electronic assemblies, specified by RTI and UL 94 rating.^3,4
• Healthcare and food-service equipment: sulfones that must withstand repeated steam sterilisation or hot water.⁵
• Chemical processing and sealing: PTFE gaskets, packings and seals, and PPS components, where the grade's chemical-resistance data fit the service.^4,7
• Protective and reinforcing fibres: aramids.⁶

How to choose: the real trade-offs

Selecting a high-performance polymer is rarely about finding the "best" one. It is about which compromise a part can live with.

• Which temperature rating applies? A part carrying load near its Tg behaves differently from a part that only needs to survive long, hot ageing. Match the RTI column (electrical, mechanical, impact) to the failure you are guarding against.
• Chemical environment. Chemical resistance depends on the polymer chemistry, the reagent and its concentration, temperature, exposure time, applied or residual stress, and the specific grade. Use the manufacturer's chemical-resistance data for the grade in question and confirm it under service conditions; family-level rankings are only a starting point.
• Processing difficulty. Victrex recommends a melt temperature of 375 °C and a mould temperature of 170–200 °C for PEEK 450G.¹ Tooling, heating and drying for those conditions add cost well beyond the resin price.
• Form available. Some of the most thermally stable materials are not injection-moulding resins at all. Kapton HN is a film,² Kevlar is a fibre,⁶ and PTFE resins are compression-moulded or extruded and then sintered.⁷
• Whether a polymer is the right answer. For some uses, metals or glass remain simpler. Our guides to borosilicate, soda-lime and quartz glass and to stainless steel versus plastic and glass walk through those comparisons for everyday containers.

What is changing: additive manufacturing

High-performance polymers are hard to 3D print for the same reasons they are hard to mould: high processing temperatures, high melt viscosity and, for semicrystalline grades, crystallinity that depends on the thermal history of each layer.

A 2023 study of three PAEK polymers printed by material extrusion and laser powder bed fusion found that inter-layer strength is still not well understood, and reported markedly lower tensile strength in the build direction than along the printed roads.¹⁰ Post-processing is one response. A 2025 study in Progress in Additive Manufacturing annealed printed PEKK at 210 °C for 30 minutes and reported crystallinity rising from 1.6% to 28.9%, with tensile strength up 29.5% and heat deflection temperature up 51.4 °C.¹¹

Polyimides are the harder case. A 2026 critical review in Progress in Polymer Science notes that their high melting temperature, high melt viscosity and narrow processing window make shaping difficult. It surveys vat photopolymerisation, material extrusion, direct ink writing and material jetting, and identifies thermoplastic polyimides as key candidates because they can be processed as melts.¹²

What is changing: the EU PFAS restriction and fluoropolymers

Status as of 15 September 2026. This section describes a regulatory process that is still under way. It is not compliance advice.

• Proposal: the Netherlands, Germany, Denmark, Sweden and Norway submitted a proposal to restrict PFAS as a group under the EU REACH regulation in January 2023. It was consulted on from March to September 2023, and an updated restriction report followed in June 2025.¹³
• Committee opinions: ECHA's Committee for Risk Assessment (RAC) adopted its opinion on 2 March 2026. The Committee for Socio-Economic Analysis (SEAC) agreed a draft opinion on 10 March 2026.¹³
• Consultation: the 60-day consultation on SEAC's draft opinion closed on 25 May 2026.¹³
• Now: SEAC is considering the consultation input, and its final opinion is expected by the end of 2026.¹³
• Next: once ECHA's committees have finished, the opinions go to the European Commission, and the decision on any restriction is taken by the Commission together with EU Member States under the REACH procedure.¹⁴
• Status: the universal PFAS restriction is not yet adopted law.

Fluoropolymers such as PTFE are among the substances discussed in the committee opinions.¹⁵ How, and on what timetable, any restriction would apply to specific fluoropolymer uses will only be known once a final text is adopted. Anyone specifying fluoropolymers for EU markets should follow that final text rather than any summary, including this one.

The short version

"High-performance" describes a combination: long-term heat resistance, chemical durability and often flame resistance, paid for with harder processing and higher cost. Start from the failure you are designing against, then read the grade's own data sheet for the matching test.

Sources

1. Victrex, VICTREX PEEK 450G technical data sheet.
2. Qnity Electronics, DuPont Kapton HN polyimide film data sheet (QE-10206, 03/26).
3. SABIC, ULTEM Resin 1000 technical data sheet (revision 20260625); SABIC, ULTEM resin.
4. Syensqo, Ryton PPS properties.
5. Syensqo, Radel PPSU properties, Radel PPSU and Radel R-5000 NT.
6. Arclin, Kevlar and "Arclin completes acquisition of the DuPont Aramids business, including iconic Kevlar and Nomex brands".
7. Chemours, Teflon PTFE fluoropolymer resins product information (C-10152, 2024).
8. UL Prospector, Relative Temperature Index (RTI), UL 746.
9. PTLI, UL thermal indexing, UL 746B.
10. T. Yap, N. Heathman, T. Phillips, J. Beaman, M. Tehrani, "Additive manufacturing of polyaryletherketone (PAEK) polymers and their composites", Composites Part B: Engineering 266 (2023) 111019.
11. F. Malekpour, M. Hojjati, "Crystallization engineering of 3D-printed PEKK: rapid post-processing route for superior strength and thermal stability", Progress in Additive Manufacturing 10 (2025) 11611–11626.
12. P. Kothavade, A. Kafi, K. Shanmuganathan, S. Bateman, "High performance polyimides for additive manufacturing: a critical review", Progress in Polymer Science 172 (2026) 102055.
13. European Chemicals Agency, "ECHA's update on the REACH restriction on PFAS", presented to the EFSA Advisory Forum, 11 June 2026.
14. CMS, "Support for EU-wide PFAS restriction with targeted derogations: what happens next?", 8 April 2026.
15. White & Case, "Europe's PFAS restriction proposal is moving forward", 13 April 2026.

Image: repeat units of PEEK and of the polyimide made from PMDA and ODA, drawn by The Calculated Chemist. Kapton, ULTEM, Radel, Ryton, Victrex, Teflon and Kevlar are trademarks of their respective owners.