Engineering Polymers in 3D Printing

High-performance engineering polymers—PEEK, PEKK, and ULTEM (PEI)—are increasingly used in aerospace, defense, and medical applications where parts need to survive demanding thermal, chemical, and mechanical environments. 3D printing these materials opens design possibilities that injection molding and machining cannot match, but the process is significantly more complex than printing standard thermoplastics like ABS or nylon.

This article covers what engineers and procurement teams need to know about printing PEEK, PEKK, and ULTEM: material properties, process requirements, design considerations, and how to evaluate supplier capability.

Why Engineering Polymers Matter

Standard 3D printing polymers (PLA, ABS, PETG, nylon) are adequate for prototyping and low-stress applications, but they fail in environments that demand high continuous service temperatures, chemical resistance, flame retardancy, or structural performance under sustained load. Engineering polymers fill this gap.

In aerospace and defense, these materials replace metal in applications where weight savings, electrical insulation, radar transparency, or corrosion immunity are drivers. Brackets, ducting, connectors, housings, and interior components are common applications. In medical, PEEK implants and surgical guides are established applications where biocompatibility and sterilization compatibility are required.

The ability to 3D print these materials means that low-volume, complex-geometry parts can be produced without the tooling investment of injection molding—which matters for defense programs with quantities in the tens or hundreds, not tens of thousands.

PEEK (Polyether Ether Ketone)

PEEK is the benchmark high-performance semicrystalline thermoplastic. Its key properties include:

Continuous service temperature: up to 250°C (480°F), with short-term excursions to 300°C. This exceeds most other printable polymers by a wide margin.

Mechanical performance: tensile strength of 90–100 MPa, flexural modulus of 3.5–4.5 GPa, and excellent fatigue and creep resistance. PEEK maintains mechanical integrity at elevated temperatures where most polymers soften dramatically.

Chemical resistance: resistant to most solvents, fuels, hydraulic fluids, and cleaning agents used in aerospace and defense environments. Only concentrated sulfuric acid attacks PEEK at room temperature.

Flame, smoke, and toxicity (FST): PEEK meets stringent FST requirements for aircraft interior applications per FAR 25.853 without flame-retardant additives.

Printing challenges: PEEK requires print temperatures of 370–420°C, build chamber temperatures of 120–200°C, and heated build plates at 150–200°C. Achieving proper crystallinity during printing is critical—amorphous PEEK has significantly lower chemical resistance and reduced mechanical properties at elevated temperatures. Chamber temperature control is the primary factor in managing crystallinity.

PEKK (Polyether Ketone Ketone)

PEKK is closely related to PEEK but offers some advantages for 3D printing:

Wider processing window: PEKK has a lower melting temperature (300–360°C depending on grade) and slower crystallization kinetics than PEEK, which makes it more forgiving to print. The slower crystallization reduces warping and internal stress during printing.

Tunable crystallinity: PEKK is available in amorphous and semicrystalline grades. Amorphous PEKK is easier to print and has better layer adhesion (important for mechanical performance in the Z-direction), while semicrystalline PEKK offers better chemical resistance and elevated-temperature performance.

Comparable performance: semicrystalline PEKK has continuous service temperature, mechanical properties, and chemical resistance comparable to PEEK. Amorphous PEKK trades some elevated-temperature performance for improved printability and interlayer bonding.

Aerospace adoption: PEKK has been adopted by several major aerospace programs, and materials like Kepstan PEKK and Antero (Stratasys PEKK filament for FDM) have established qualification databases. PEKK is used in structural brackets, ducting, and secondary structures where weight savings over aluminum are significant.

ULTEM (PEI – Polyetherimide)

ULTEM is the trade name for polyetherimide (PEI), produced by SABIC. Two grades are most common in 3D printing:

ULTEM 9085: The most widely used grade for aerospace FDM printing. It is FST-compliant per FAR 25.853, has a continuous service temperature of ~170°C, and is amorphous (no crystallinity concerns during printing). ULTEM 9085 has extensive flight qualification data and is the standard material for many airline interior components produced by additive manufacturing.

ULTEM 1010: Higher temperature capability (~216°C continuous) and better chemical resistance than 9085, but more difficult to process and with less qualification data for aerospace applications. Used for tooling, fixtures, and autoclave-capable manufacturing aids.

Advantages for aerospace: ULTEM's key advantage is its extensive qualification history. FAA-accepted flamability data, a large database of mechanical properties across temperature and environmental conditions, and documented aging behavior make ULTEM lower-risk than newer materials for certification-driven programs. It is also easier to print than PEEK or PEKK—typical print temperatures are 340–380°C with chamber temperatures of 130–170°C.

Limitations: ULTEM's mechanical properties and temperature resistance are lower than PEEK and semicrystalline PEKK. As an amorphous polymer, ULTEM also has lower chemical resistance than semicrystalline PAEK-family materials.

Comparing the Three Materials

For a buyer evaluating these materials for a specific application, the decision typically comes down to three factors:

Temperature requirement: If the part must survive above 200°C continuously, PEEK or semicrystalline PEKK are the options. Below 170°C, ULTEM 9085 is usually the lowest-risk choice due to its qualification history.

Certification path: If the program requires an existing qualification database and FAA flamability data, ULTEM 9085 has the most established path. PEKK is growing in qualification data. PEEK has excellent intrinsic properties but less standardized AM qualification data for aerospace.

Mechanical performance: PEEK and semicrystalline PEKK offer the highest strength, stiffness, and fatigue resistance. For structural applications at elevated temperatures, these are the leading candidates. ULTEM is adequate for secondary structures and non-load-bearing applications.

Process and Supplier Evaluation

When sourcing 3D-printed engineering polymer parts, the supplier's process control is at least as important as their material selection. Key evaluation criteria include:

Machine capability: printing PEEK, PEKK, and ULTEM requires industrial-grade machines with high-temperature extruders, heated chambers, and controlled cooling. Consumer or prosumer machines cannot reliably print these materials. Ask about specific machine models, temperature ranges, and build volume.

Material handling: PEEK and PEKK are hygroscopic—moisture absorption before or during printing causes defects, porosity, and degraded mechanical properties. Suppliers must demonstrate controlled material drying, storage, and handling procedures.

Crystallinity control: For PEEK and semicrystalline PEKK, ask how the supplier manages crystallinity during printing. What chamber temperature do they use? Do they perform post-print annealing? How do they verify crystallinity (DSC testing)? Amorphous regions in parts specified as semicrystalline will have reduced chemical resistance and elevated-temperature performance.

Mechanical testing: Request test data for parts printed in the build orientation relevant to your application. Z-direction (interlayer) properties are always lower than X-Y properties for FDM parts. If the part is loaded primarily in the Z-direction, this must be accounted for in design and validated by testing.

Quality system: For aerospace applications, the supplier should operate under AS9100 or an equivalent quality system with documented process controls, material traceability, and inspection procedures. For medical applications, ISO 13485 applies.

Engineering polymer 3D printing occupies a specific and growing niche in aerospace, defense, and medical manufacturing. The materials offer properties that bridge the gap between standard plastics and metals, and additive manufacturing makes them accessible for complex geometries at low volumes. Success depends on matching the right material to the application's thermal, mechanical, and certification requirements—and on selecting a supplier with the process control to deliver consistent, qualified parts.

Explore Our Capabilities

Learn more about how Metal Powder Supply supports aerospace and defense manufacturing:

• Additive Manufacturing

Need a quote or have questions about your project? Request a quote or contact our team to discuss your requirements.