ESD PEI and ESD PEEK are the two antistatic engineering plastics that electronics and semiconductor plants choose between, and the difference between them is not the static control but the base resin. Both are polyetherimide (PEI) and polyetheretherketone (PEEK) compounded with a conductive filler such as carbon fibre, carbon black or carbon nanotubes, so both reach the same dissipative band (106–109 Ω/sq) and overlap closely in the conductive range (103–106 Ω/sq). Where they split is everything the base resin decides. ESD PEI is the economical one — glass transition ~217°C, continuous service ~170°C, high stiffness and dielectric strength, at roughly half the material cost of PEEK. ESD PEEK is the high-performance one — melting point 343°C, continuous service 260°C, water absorption 0.07%, outstanding resistance to solvents, superheated steam and plasma, and the wear resistance to run loaded, moving parts. Rule of thumb: below roughly 150°C in benign chemistry, ESD PEI does the job for about half the money; from 180°C upward, or wherever chemicals, steam, plasma or wear set the limit, only ESD PEEK holds.
Antistatic parts fail for two different reasons — the static control is wrong, or the base resin is wrong — and we machine both materials in-house, so this comparison quotes the differences that decide real projects rather than the ones that look good on a datasheet.
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● Quick Answer >> Head-to-Head Table >> What "ESD Grade" Really Means >> Heat Resistance: The Decisive Split >> Chemicals, Steam and Wear >> Cleanroom Realities >> Cost and Availability >> When Each One Wins >> FAQ
Pick ESD PEI when the part lives below roughly 150°C, sees no aggressive chemistry, steam or plasma, and cost per part drives the project — electronics handling fixtures, IC test sockets, trays, covers and handler components. It typically lands at about half the cost of ESD PEEK.
Pick ESD PEEK when the part runs hot (180–260°C), meets plasma, solvents or superheated water, or has to wear or carry load while it dissipates charge.
When both fit the drawing, the deciding questions are the two checklists at the end of this article — and we will tell you when the cheaper one is enough, because we quote both.
| Property | ESD PEI (typical) | ESD PEEK (PRES stock grades) |
|---|---|---|
| Base polymer | PEI / ULTEM, amorphous | PEEK, semi-crystalline |
| Glass transition (Tg) | ~217°C | 143°C |
| Melting point | None (amorphous) | 343°C |
| Continuous service | ~170°C | 260°C (300°C short-term) |
| HDT (1.8 MPa, filled) | ~205°C (GF30) | ~325°C (fiber-filled) |
| Surface resistivity — dissipative | 106–109 Ω/sq | 106–109 Ω/sq |
| Static decay (typical) | less than 2 s | less than 2 s |
| Tensile strength | ~105 MPa unfilled / ~150 MPa GF30 | 100 MPa unfilled / 175–260 MPa filled |
| Flexural modulus | ~3.2 GPa unfilled / ~9 GPa GF30 | 4.1 GPa unfilled / 11–23 GPa filled |
| Water absorption (24 h) | ~0.25% | 0.07%~0.04(filled) |
| Chemical resistance | Good; stress-cracking is the watch item | Excellent, including steam and hydrolysis |
| Wear / bearing duty | Moderate | Excellent (bearing-type ESD grades available) |
| Relative cost | $$$ | $$$$$ |
PEEK values are PRES stock-grade data. ESD PEI and filler-system figures are industry typical values for consolidated grades — the producer's TDS governs. Surface resistivity varies strongly with test method, surface finish and lot, so verify on the measured surface.
Neither PEI nor PEEK is conductive on its own. Unfilled, both sit above 1015 Ω/sq — solid insulators. Static control arrives through a filler network: carbon fibre, carbon black or carbon nanotubes, loaded until the particles touch and give charge a path to ground. That is why two chemically unrelated resins can quote identical resistivity numbers — and why the resistivity you get is a property of the compound, not of the plastic family.
Insulative (above 1012 Ω/sq) — charge accumulates and discharges when and where it wants. This is what you are trying to leave.
Dissipative / antistatic (106–109 Ω/sq) — the band most electronics handling, IC test sockets and wafer carriers specify: charge bleeds away slowly and controllably.
Conductive (103–105 Ω/sq) — for grounding paths, high-speed lines and anywhere discharge has to be immediate.
Two practical notes before choosing a family. First, resistivity is measured on a surface, and machining exposes a different fibre orientation than moulding — a machined face can read differently from the same compound as supplied. Second, check that the filler system is carbon-based rather than metal-based: metal fillers bring ionic contamination risk that most wafer and disk-media specifications refuse. Our ESD engineering plastics guide covers the full band system and how it maps to applications.
Heat resistance is where the two antistatic plastics separate first. PEI is amorphous with a glass transition near 217°C (typical) and a practical continuous ceiling around 170°C. PEEK serves at 260°C continuously with 300°C short-term peaks. The interesting zone is between roughly 150°C and 180°C, where ESD PEI still looks viable on paper but has run out of headroom under load: creep accelerates, stiffness falls, and a fixture that held tolerance at room temperature starts drifting. Above that band, the question answers itself.
This matters because ESD parts are usually near heat. Reflow oven fixtures, IR preheat stations, plasma chambers, hot handlers, motor and drive enclosures, downhole and aerospace electronics — all of them put an antistatic part in a warm place. If the part sees sustained service above ~150°C, or has to survive brief excursions past 200°C, ESD PEEK is the only one of the two that keeps its dimensions through the cycle.
Cleaning chemistry is the second divider. PEI is attacked by strong bases and some chlorinated solvents, and it stress-cracks under load in aggressive media — a real constraint in fabs where solvent and alkaline cleaning is routine. PEEK resists that map plus superheated water and steam, which is why ESD PEEK owns plasma etch hardware, wet-bench fixtures and any part that gets steam-sterilized between runs.
Wear is the third. PEI is dimensionally stable and low-creep, but it is not a bearing material. PEEK is available as a bearing-type ESD grade that combines the conductive network with PTFE and graphite, so the part dissipates and slides in the same compound — for sliding contacts, wear strips or dry-running bearings under ESD control, that combination has no PEI equivalent — it is stocked as ESD PEEK rods and cut or machined to your drawing. Grade-level detail sits in our PEEK grade selection guide.
Particulate shedding — carbon-filled compounds release black debris at abrasion points. The tougher the wear behaviour, the less debris, which favours PEEK wherever surfaces rub.
Outgassing — for vacuum and plasma hardware, specify low-outgassing material. PEEK keeps extractables low even near its ceiling, where PEI is already at the edge of its range.
Metal-free fillers — confirm the conductive system is carbon-based. Metal-based fillers risk ionic contamination on wafers and disk media.
Cleanliness after machining — ESD parts should be machined and cleaned without lubricants that leave residue; a contaminated surface reads as a different resistivity than the datasheet — which is why fixture and tray work typically starts from ESD PEEK sheet, machined and cleaned dry.
If your requirement includes any of the above, two pages go deeper: our high-purity, low-extractable ESD PEEK notes and the ESD PEI granules data for yield-critical lines. If you are still deciding whether a PEEK part needs an ESD grade at all, start with is PEEK material ESD?
ESD PEI stock shapes generally land at roughly half the cost of ESD PEEK, sometimes less. A filled ESD PEI part that meets the specification is money saved, and paying for temperature headroom you will never use is the most common overspend we see on antistatic projects. The reverse also holds: an ESD PEI part that creeps at 180°C, cracks in solvent or wears through is not a saving at all — it is a line stop with a purchase order attached.
Both materials are extruded and machined in-house here, in rod, sheet, tube and profile, and cut to your drawing. Send us the target surface resistivity band, the service temperature and the medium, and we will quote the resin the part actually needs — including the cheaper one. If the part is moulded rather than machined, the same resistivity band is met in ESD PEEK granules (injection grade).
ESD PEI wins when:
Continuous temperature stays below ~150°C, with no steam, plasma or aggressive solvent.
The part is a precision fixture, test socket, tray, cover or handler component where dimensional stability matters more than toughness.
Cleaning chemistry is mild and stress cracking is not a risk.
Volume is high and cost per part drives the project.
ESD PEEK wins when:
Service reaches 180–260°C, or brief excursions past 200°C are part of the process.
Plasma, solvents, superheated water or steam touch the part.
The part slides, wears or carries load while it dissipates.
Contamination, outgassing or extractables are tightly specified.
Full property data for the PEEK side is on our PEEK material page, the PEI side on our PEI material page, and ESD grade selection rules for semiconductor work in our antistatic PEEK selection guide.
Q1: Can ESD PEI replace ESD PEEK?
A: Often, yes — and we will say so at quotation stage. If the part stays below ~150°C, sees only mild chemistry, does not steam or plasma, and does not wear, ESD PEI delivers the same resistivity band at roughly half the cost. Above that temperature, or with chemicals, steam or wear in the picture, PEEK holds the line.
Q2: Which one has better static control?
A: Neither, by polymer. Both reach dissipative (106–109 Ω/sq) and conductive (103–106 Ω/sq) bands; the filler loading decides the band and the base resin decides everything else. Judge the two materials on temperature, chemistry and wear, then set the resistivity band separately.
Q3: What surface resistivity do I actually need?
A: For most electronics handling, test sockets and wafer carriers, 106–109 Ω/sq dissipative is the specified band: charge drains controllably without the fast discharge of a conductor. Choose 103–105 Ω/sq conductive only where the part is a grounding path or speed of discharge is critical.
Q4: Do ESD grades sacrifice mechanical strength?
A: It depends on the filler. Carbon fibre raises stiffness and strength but reduces elongation and impact toughness; carbon black or nanotube systems keep far more toughness while typically landing in the dissipative band rather than the conductive one. Specify the mechanical requirement and the resistivity band together, not one after the other.
Q5: Are ESD PEI and ESD PEEK safe for wafers and disk-drive parts?
A: With carbon-based, metal-free fillers, both are used in these environments — PEEK where temperature, plasma or extractables are demanding, PEI where they are not. Verify three things on the certificate: filler system, measured surface resistivity on a machined surface, and outgassing or extractables data if the part enters a chamber.
Not Sure Which ESD Grade Your Part Needs?
Send the drawing, the target surface resistivity band and the service temperature — we machine both materials in-house and will tell you when the cheaper one is enough.
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