Application of ULTEM/PEI high-performance thermoplastics to 3D printing

ULTEM is Sabic's trade name for polyetherimide, usually shortened to PEI. It is an amorphous polymer, not semi-crystalline like PEEK or PPS. That single structural difference explains most of its behavior: it softens gradually instead of melting at a sharp point, it bonds well between layers, and it holds tighter tolerances after printing than semi-crystalline grades. Glass transition sits around 217 °C, and unfilled PEI carries a continuous service temperature near 170 °C.

The common printing grades are ULTEM 9085 (PEI blended with polycarbonate copolymer) and ULTEM 1010 (unfilled PEI). 9085 is the workhorse for aerospace interior brackets and ducting because it passes FAR 25.853 flammability and smoke tests and prints with better layer adhesion. 1010 is stiffer and has higher temperature resistance, so it suits tooling, electrical housings and sterilizable fixtures. Both are available in natural amber and black.

Mechanically, PEI is not a replacement for aluminum or PEEK. Tensile strength lands in the 70–110 MPa range depending on grade and build orientation, but the interlayer direction is always the weak axis. A printed bracket can be 30–50 percent weaker across the Z direction than in-plane. Design for that, or plan a secondary machining step.

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  AmorphousLow warpage, good layer bonding, transparent-ish amber color
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  Service temperatureRoughly 150–170 °C continuous for unfilled PEI
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  ChemistryResists fuels, oils, alcohols and many solvents; attacked by strong bases
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  ElectricalsStable dielectric constant across temperature and frequency

PEI prints hot. Nozzle temperature typically runs 360–400 °C, and the chamber has to be held at 150–200 °C for the whole build. That is not a comfort setting. A cold chamber means the deposited bead freezes before the next layer arrives, and the part delaminates along layer lines. Any machine without an actively heated chamber above 150 °C will produce weak PEI parts regardless of the slicer profile.

Layer height usually sits between 0.2 mm and 0.4 mm. Thinner layers improve surface finish and Z strength but slow the build and raise the risk of heat soak in small features. Print speed is low by FDM standards, often 20–40 mm/s, because the extruder is fighting a high-viscosity melt. Nozzle diameter of 0.4–0.6 mm is typical; going smaller invites clogging with glass-filled grades.

Bed adhesion is handled with a dedicated high-temperature build plate or a PEI-compatible sheet held near 160 °C. Do not expect standard glue stick workflows to survive. Support material matters too: breakaway support leaves witness marks on sealing faces, while soluble support is the cleaner route for internal channels but adds post-processing time and cost.

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  Nozzle360–400 °C, hardened nozzle for glass-filled grades
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  Chamber150–200 °C, actively controlled for the full build
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  Layer height0.2–0.4 mm; thinner improves Z strength, slows the job
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  OrientationKeep tensile and bending loads in the XY plane

PEI suits parts with a moderate footprint and walls between 2 mm and 5 mm. Thin walls below 1.5 mm cool too fast and curl at the corners; thick sections above 8 mm trap heat and produce internal porosity that only shows up after annealing. If a design calls for a solid block, hollow it with a lattice or print it in two halves and bond them.

Avoid large unsupported overhangs beyond about 45 degrees. PEI sags noticeably when the chamber is at 180 °C, more than ABS does at 100 °C. Chamfers beat fillets on downward-facing edges because the extruder has less material to lay on air. Horizontal holes print oval, so drill or ream them after the build if they carry a fastener.

For load-bearing joints, add bosses with generous radii and keep fasteners in the XY plane. A bolt that pulls layers apart will fail at a fraction of the material's rated strength. Where a printed PEI part must meet a tolerance tighter than about ±0.3 mm, plan a finish machining pass on the critical faces rather than chasing it with slicer compensation.

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  Wall thickness2–5 mm is the sweet spot for strength and stability
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  OverhangsKeep below 45 degrees; use chamfers, not fillets
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  HolesPrint undersize and ream; expect ovality from sag
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  Tolerances±0.3 mm as-printed; tighter needs CNC finishing

Annealing is not optional for parts that see heat. As-printed PEI holds residual stress from the rapid cooling of each bead, and when the part later sees 150 °C in service it can distort or crack along layer lines. A staged anneal, ramping slowly to roughly 200 °C and holding before a controlled cool-down, relieves that stress. Ramp rates of 1–2 °C per minute are common; faster ramps reintroduce the problem you are trying to solve.

Expect shrinkage during annealing. Amorphous PEI moves less than semi-crystalline PEEK, but a 100 mm part can still shift by a millimeter or more. Print oversize on critical dimensions, or anneal a near-net blank and machine it afterward. For parts that need both temperature resistance and tight geometry, the practical route is print, anneal, then CNC the mating faces, bores and sealing surfaces.

Finishing options are limited compared with metal. Vapor smoothing is not standard for PEI and solvent polishing is risky. Bead blasting gives a uniform matte surface and hides layer lines on non-critical faces. Laser marking works for part numbers and traceability codes. If the part needs a conductive or EMI-shielding surface, that has to come from a coating, not from the base polymer.

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  Anneal ramp1–2 °C per minute to about 200 °C, then controlled cool
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  ShrinkagePrint oversize; expect roughly 0.5–1.5 percent movement
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  Hybrid routePrint, anneal, then CNC bores and sealing faces
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  SurfaceBead blast for matte; laser mark for traceability

Printed PEI loses to machined PEI on every dimensional and strength metric that matters for a structural part. If the part is a manifold, an insulator with a critical bore, or anything that must hold ±0.005 mm, machine it from PEI stock instead. The material cost is higher, but the part is isotropic and the tolerance is real rather than nominal.

It also loses on cost for simple geometry. A printed PEI bracket with a long heated build and a slow anneal can cost more than a machined aluminum equivalent, especially at quantities above a few dozen. Printing pays off when the geometry is complex, the quantity is low, the weight matters, or the part needs PEI's dielectric and thermal properties in a shape that would be expensive to machine.

There is a middle path that often wins: print the complex PEI body, then finish the critical interfaces on a CNC. GreatLight runs both processes under one roof, with 127 high-precision CNC machines and 5-axis capacity to 4,000 mm, so the print-and-machine sequence is quoted as one job rather than two. That avoids re-fixturing surprises and keeps the tolerance chain in one inspection report.

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  Choose printingLow volume, complex shape, weight saving, dielectric needs
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  Choose machiningTight tolerance, structural load, isotropic strength, flatness
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  Choose bothPrinted body with machined bores, seats and sealing faces