PEI (ULTEM)

PEI (polyetherimide), widely known by the trade name ULTEM, is an amorphous high-performance thermoplastic. It combines high strength and stiffness with a glass transition of up to about 217 °C, inherent flame resistance with low smoke, and good dimensional stability. Two grades dominate industrial FDM printing: ULTEM 9085, a PEI-based blend developed for aircraft interiors, and ULTEM 1010, an unfilled PEI with higher heat resistance and stiffness. Unfilled and glass-filled PEI is also available as rod and plate for CNC machining.

Choose PEI when a part must stay stiff above the roughly 120 °C at which PC and most nylons reach their limit, when flame, smoke and toxicity (FST) requirements apply, or when a light polymer should replace metal in fixtures and tooling. Its limits: printed parts are much weaker across the layers, PEI is attacked by chlorinated solvents and strong alkalis, and it costs several times more than standard engineering plastics. On Uretyco, PEI is offered through partners with industrial heated-chamber FDM printers and for CNC machining; grade, feasibility and lead time are confirmed during quote and order review.

Mechanical and physical properties

FDM printing PEI

PEI is printed only on industrial FDM systems with a heated build chamber, which keeps the part hot throughout the build so that layers fuse and large parts do not warp. Supports are usually a breakaway material removed by hand, and layers are typically about 0.25–0.33 mm, so fine detail and small text come out coarser than on desktop materials. Because PEI is amorphous, printed parts need no crystallization step after printing. Design and ordering points:

• Orientation: across-layer strength is often about 40% lower than in-plane strength. Keep the main load path, clips and bosses in the layer plane, and state a fixed orientation in the order notes.
• Walls and features: plan walls of at least about 1.0–1.5 mm, several extrusion widths thick. Very thin ribs, pins and sharp edges print poorly with the wide beads used for PEI.
• Fill: ask for solid parts where strength or airtightness matters; sparse interiors save material and build time on large tools and fixtures.
• Supports and cosmetic faces: surfaces more than about 45° from vertical need supports, which leave marks. Mark faces that must stay clean, and avoid closed channels from which supports cannot be removed.
• Holes and threads: drill or ream fit-critical holes after printing and use threaded inserts for repeated assembly; printed threads suit low loads only.

CNC machining PEI

PEI rod and plate machine cleanly with sharp carbide tools and give stable, accurate parts, which suits insulators, test sockets, fluid manifolds and fixtures in small quantities. Unfilled PEI is a translucent amber; 30% glass-filled grades are stiffer and more dimensionally stable but abrasive. As an amorphous polymer, PEI is prone to stress cracking when it meets the wrong fluids. Watch for:

• Coolants and cleaners: use air or a compatible water-based coolant. Chlorinated solvents and some aggressive cleaners can cause crazing, sometimes days after machining.
• Stress and stability: use stress-relieved stock and keep tools sharp; for tight tolerances, rough-machine, anneal, then finish.
• Glass-filled grades: they wear tools quickly; carbide is the minimum, and diamond-coated tools last much longer on batches.
• Walls, corners and threads: start from the CNC Design Guide's plastic values (1.5 mm minimum wall, internal radii at least one-third of the pocket depth). Tapped threads work in unfilled PEI; use threaded inserts for repeated assembly or glass-filled grades.

Tolerances and surface

Without a drawing tolerance, FDM parts on Uretyco follow the default of ±0.5 mm or ±0.5%, whichever is greater; actual results vary with orientation, part size, supports and post-processing, and tighter values on well-supported features need a drawing and acceptance in the quote; long, flat or thick parts can deviate more, so machine critical bores and datum faces after printing. For machined PEI, Uretyco treats unspecified tolerances as ISO 2768-mK, with a default surface of about Ra 1.6–3.2 µm; tighter tolerances need a 2D drawing. Final values are confirmed in the quote and order review.

Finishing options

Most PEI parts are used as printed or as machined. Finishing removes support marks, smooths cosmetic or airflow surfaces and adds accurate machined features; on interior parts, every coating must suit the part's flame, smoke and toxicity requirements.

Cost and lead-time drivers

PEI filament and stock cost several times more than ABS or PC, and only printers with heated chambers can process the filament, so material and machine time both weigh heavily. The main levers:

• Build volume and height: large solid parts mean long builds on high-temperature printers; sparse fill on non-critical tooling shortens them.
• Supports and orientation: breakaway supports add material and manual removal, so an orientation that needs fewer supports lowers cost and improves surfaces.
• Grade and traceability: certified versions of 9085 and 1010 with lot traceability are specialty items; request them at quote time so availability and lead time can be confirmed.
• Machining stock: design machined parts around standard rod and plate sizes; glass-filled grades add tool wear.
• Documents: material certificates and a certificate of conformance are opt-in and can extend the lead time. Request them at quote time.

PEI vs. other high-performance plastics

PEI is the practical choice when flame behavior, heat resistance up to about 170 °C and a reliable printing process matter together. Move to PEEK or PEKK for higher continuous temperatures and aggressive chemicals, and to PC when neither heat nor flame requirements justify the price of PEI.

When not to choose PEI

Typical applications

• Aircraft interior parts such as ducts, brackets, covers, panels and clips, mostly in 9085 and subject to qualification.
• Composite layup tools, trim fixtures and drill guides that see oven or autoclave temperatures, mostly in 1010.
• Jigs, fixtures and gauges used near ovens, welding cells and molding machines.
• Electrical insulators, connectors, test sockets and coil formers machined from stock.
• Low-volume interior parts for rail and other transport, subject to the applicable fire standard such as EN 45545-2.

Specifying PEI on Uretyco

1. 1
   Upload STL, 3MF or STEP

   STEP is preferred for machined parts and for printed parts that get machined features; add a 2D drawing for critical tolerances and threads.

2. 2
   Choose the process and grade

   FDM in 9085 for interior and general functional parts, or in 1010 for the highest heat resistance; CNC in unfilled or 30% glass-filled stock. Name the grade in the order notes.

3. 3
   State the requirements

   Give the service temperature, loads, chemicals and any flame, smoke and toxicity requirement, so that grade and build strategy fit the application.

4. 4
   Mark orientation and critical faces

   Note the main load direction, cosmetic faces that supports must not touch, and features to be drilled, reamed or machined.

5. 5
   Request documents and review the quote

   Ask for certified material, lot traceability or a certificate of conformance at quote time; feasibility, grade and lead time are confirmed in the quote and order review.

FAQ

ULTEM 9085 or ULTEM 1010?

Choose 9085 for most functional and interior parts: it is tougher, less brittle and the grade most often used where FST requirements apply. Choose 1010 when heat resistance and stiffness matter more, for example for composite layup tools or fixtures above about 150 °C; it is stronger and stiffer but more brittle. Both print on the same class of heated-chamber printers.

Does printed PEI meet aircraft flammability requirements?

Material suppliers publish data showing that 9085 can meet the flammability, heat release and smoke density tests of FAR 25.853 and the toxicity limits set by aircraft manufacturers. Whether a specific part complies depends on the material lot, wall thickness, geometry, finish and test method, and it is shown through your own qualification. State the requirement and the documents you need at quote time.

Can PEI be used for food-contact or medical parts?

PEI is used in both fields, and some PEI filaments and stock grades come with material-level documentation for food contact or biocompatibility, such as testing to ISO 10993. That documentation covers the material, not the finished part: printed layer seams can trap residues, and compliance depends on the exact certified grade, process validation and your own regulatory responsibility. State the intended use in the order notes so that feasibility can be reviewed.

PEI or PEEK?

PEI is easier to print, amorphous and usually less expensive; it suits parts up to about 170 °C that need flame resistance and good stiffness. PEEK costs more but handles continuous temperatures up to about 250 °C, hot water, steam and aggressive chemicals. For printed parts beyond the heat range of PEI, PEKK often prints more reliably than PEEK.

Related resources

• PEEKFor continuous use up to about 250 °C and aggressive media.
• PEKKPAEK polymer that prints more easily than PEEK.
• Polycarbonate (PC)Lower-cost choice up to about 125 °C.
• 3D PrintingTechnologies, files and cost drivers.
• CNC Design GuideTolerances, walls, threads and setups.
• Certificates & Inspection ReportsMaterial certificates, conformance and inspection documents.