PEEK and PEI sit at the top of the filament range. 3DXTech describes all three grades on this page as inherently flame resistant; all print at nozzle temperatures far beyond most desktop hotends and need a bed well above 100 °C. 3DXTech says most standard desktop printers cannot reliably hold the conditions PEEK needs, and describes PEI as typically printing more predictably.
This page uses 3DXTech's ThermaX data sheets for PEEK and for two PEI grades, made from SABIC's ULTEM 1010 and ULTEM 9085 resins. The PEI grades differ: 1010 has the higher glass transition and stiffness, while 9085 is the grade Stratasys says meets aerospace and railway flame, smoke and toxicity standards. All values are for flat X-Y specimens printed on an open-source FDM printer; 3DXTech reports no Z-direction or impact values.
PEEK and PEI side by side
| Property | PEEK | PEI |
|---|---|---|
| Nozzle temperature | 400–480 °C in 3DXTech's print table; its description says to plan on a 360–450 °C hotend | 350–380 °C (PEI 9085); 370–390 °C (PEI 1010) (3DXTech) |
| Bed temperature | 140–180 °C in the print table; 120–160 °C in the description (3DXTech) | 140–160 °C (PEI 9085); 120–160 °C (PEI 1010) (3DXTech) |
| Heated chamber | Recommended, 70–140 °C if possible; description: fully enclosed and actively heated, 70–150 °C | Recommended; no temperature given (3DXTech) |
| Drying | 150 °C for 3 h (3DXTech drying instructions) | 130 °C for 4–6 h (PEI 9085); 150 °C for 4–6 h (PEI 1010) |
| Data sheet specimen settings | 380–400 °C nozzle, 130–140 °C bed | 365–385 °C (9085) or 380–400 °C (1010) nozzle; 130–140 °C bed |
| Tensile strength, ISO 527 | 100 MPa | 54 MPa (9085); 56 MPa (1010) |
| Tensile modulus, ISO 527 | 3720 MPa | 2050 MPa (9085); 2500 MPa (1010) |
| Tensile elongation, ISO 527 | 28% | 3% (both grades) |
| Flexural strength / modulus, ISO 178 | 130 / 2700 MPa | 90 / 2170 MPa (9085); 110 / 2510 MPa (1010) |
| Glass transition (DSC) | 143 °C | 186 °C (9085); 217 °C (1010) |
| Heat deflection, ISO 75 at 0.45 MPa | 140 °C | 158 °C (9085); 208 °C (1010) |
| Melting point and continuous use | Melting point 343 °C; continuous use temperature 240–260 °C (3DXTech product page) | Not stated; 3DXTech describes PEI as amorphous |
| Flammability, UL 94 (base resin) | V-0 at 1.5 mm | V-0 at 1.5 mm (both grades) |
| Density, ISO 1183 | 1.30 g/cm³ | 1.34 g/cm³ (9085); 1.27 g/cm³ (1010) |
Property values come from 3DXTech's ThermaX PEEK (Rev 3.0), ThermaX PEI 1010 and ThermaX PEI 9085 (Rev 4.0) technical data sheets: ISO methods, 0.4 mm nozzle, 0.25 mm layers, 100% infill at ±45°, X-Y flat specimens. Print settings come from 3DXTech's product pages and drying instructions; the flame, smoke and toxicity note comes from Stratasys's ULTEM 9085 data sheet.
Strength and ductility
The mechanical gap is large. 3DXTech lists 100 MPa tensile strength and 28% elongation for ThermaX PEEK, against 54 to 56 MPa and 3% for its two PEI grades. PEEK is also the stiffest of the three in tension (3,720 MPa) and the strongest in bending (130 MPa).
These figures come from flat X-Y specimens only. 3DXTech does not report strength across layers or any impact values, which are often where printed high-temperature parts fail, so a test print in the real orientation is worth the material cost before committing to either.
Heat: read the numbers carefully
On 3DXTech's data sheets, both PEI grades beat PEEK on short-term heat measures. PEI 1010 has a 217 °C glass transition and 208 °C heat deflection at 0.45 MPa, PEI 9085 186 °C and 158 °C, and PEEK 143 °C and 140 °C.
PEEK's product page adds a 343 °C melting point and a continuous use temperature of 240 to 260 °C, figures 3DXTech does not give for PEI, which it describes as amorphous. The data sheet does not say whether the PEEK specimens were annealed after printing. Because these numbers measure different things, compare them with the temperature, load and duration your part will actually see, and ask the supplier for data that matches your process.
Printer requirements
3DXTech says PEEK needs industrial printing conditions: a 360 to 450 °C hotend, a 120 to 160 °C bed and a fully enclosed, actively heated 70 to 150 °C chamber, plus slow speeds and little or no part cooling. Its print table on the same page lists higher ranges (400 to 480 °C nozzle, 140 to 180 °C bed). It also advises purging PEEK fully from the nozzle at the end of a print, because PEEK left to cool in the nozzle can cause black specks and severe clogs.
PEI asks for less: 350 to 380 °C for PEI 9085 and 370 to 390 °C for PEI 1010, with a heated chamber recommended. 3DXTech's drying instructions give 150 °C for 3 hours for PEEK, 130 °C for 4 to 6 hours for PEI 9085 and 150 °C for 4 to 6 hours for PEI 1010; the product pages list different drying values, so confirm with 3DXTech for your reel. On its PEEK page, 3DXTech suggests PEKK, PEI and PPS as alternatives that are easier to process.
Choosing a PEI grade
The two ULTEM-based filaments are not interchangeable. PEI 1010 has the higher glass transition (217 against 186 °C), heat deflection (208 against 158 °C at 0.45 MPa) and stiffness (2,500 against 2,050 MPa). PEI 9085 prints at slightly lower nozzle temperatures, and 3DXTech describes it as flame resistant with low smoke evolution and toxicity.
Stratasys says its own ULTEM 9085 filament meets several aerospace and railway standards for flame, smoke and toxicity. That certification applies to Stratasys's material and process; a third-party filament made from the same resin family should not be assumed to carry it.
Which should you choose?
Choose PEEK if…
- The part needs ductility; ThermaX PEEK's 28% elongation compares with 3% for both PEI grades.
- You need the highest tensile and bending strength 3DXTech lists among these grades.
- Long exposure to high temperature is expected and 3DXTech's 240–260 °C continuous use figure fits the case.
- Your printer can run the 360–450 °C hotend and actively heated chamber 3DXTech plans for.
Choose PEI if…
- Heat deflection under light load matters, where PEI 1010 reaches 208 °C at 0.45 MPa.
- The application calls for flame, smoke and toxicity data, which Stratasys reports for ULTEM 9085.
- You want the more predictable process 3DXTech describes for PEI.
- Your hotend tops out below PEEK's range; 3DXTech lists 350–380 °C for PEI 9085.
Common questions
Is PEEK better than PEI?
It depends on the requirement. In 3DXTech's data, PEEK is far stronger and more ductile (100 MPa and 28% elongation against 54 to 56 MPa and 3%), while PEI 1010 has the higher glass transition and heat deflection at 0.45 MPa. PEI is also the easier material to print, according to 3DXTech.
What is the difference between ULTEM 1010 and ULTEM 9085 filament?
In 3DXTech's ThermaX data, PEI 1010 has a 217 °C glass transition and 2,500 MPa tensile modulus, against 186 °C and 2,050 MPa for PEI 9085. Stratasys says its ULTEM 9085 filament meets aerospace and railway flame, smoke and toxicity standards.
Can a desktop printer print PEEK?
3DXTech says most standard desktop printers cannot reliably maintain the conditions PEEK needs. It plans for a 360 to 450 °C hotend, a 120 to 160 °C bed and a fully enclosed chamber actively heated to 70 to 150 °C.
Sources
- ThermaX PEEK technical data sheet (Rev 3.0) 3DXTech · Checked 2026-11-02
- ThermaX PEI (ULTEM 9085) technical data sheet (Rev 4.0) 3DXTech · Checked 2026-11-02
- ThermaX PEI (ULTEM 1010) technical data sheet (Rev 4.0) 3DXTech · Checked 2026-11-02
- ThermaX PEEK product page 3DXTech · Checked 2026-11-02
- ThermaX PEI 9085 product page 3DXTech · Checked 2026-11-02
- ThermaX PEI 1010 product page 3DXTech · Checked 2026-11-02
- Filament drying instructions 3DXTech · Checked 2026-11-02
- ULTEM 9085 resin data sheet Stratasys · Checked 2026-11-02
This comparison summarizes the cited documentation; it is not a lab test. Properties vary by brand, grade, print settings and orientation, so check the data sheet for the exact product you buy.