Ultem (PEI) is a high-performance thermoplastic that is known for being very strong, stable at high temperatures, and naturally resistant to flames. It stays accurate mechanically at temperatures up to 170–180°C, which is much better than most engineering plastics when it comes to heat and size stability.
Ultem is used a lot in aerospace parts, medical devices, electronic housings, and high-temperature industrial parts because it is tough, resistant to chemicals, and has great electrical properties. This guide talks about the main grades, processing methods, and engineering factors that need to be taken into account in order to use PEI effectively in tough situations.
What Is Ultem (PEI)?
Ultem plastic is a semi-transparent amber-colored polymer belonging to the polyetherimide (PEI) family, developed by General Electric (now SABIC). Chemically, it is a polyimide derivative with ether linkages in its molecular backbone, combining rigidity from the imide rings with processability from the ether segments. This unique molecular architecture gives Ultem its hallmark characteristics:
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High glass transition temperature (Tg ≈ 217°C)
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Excellent mechanical retention at elevated temperatures
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Low creep and dimensional stability under load
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Outstanding electrical insulation and flame retardancy
Because of these properties, Ultem is often used as a structural alternative to metals or thermosets, especially when weight reduction and precision are critical.
Why Ultem Is Considered an Aerospace-Grade Plastic
Few polymers can maintain mechanical integrity, low smoke generation, and electrical insulation at such high service temperatures. Ultem’s high Tg, low outgassing, and superior hydrolytic stability make it ideal for:
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Aircraft interiors (seat frames, ventilation ducts, housings)
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Avionics insulation and structural supports
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High-temperature electrical connectors and medical sterilizable components
It also offers lighter weight than aluminum with comparable stiffness-to-weight ratios in some designs, enabling engineers to achieve fuel savings and miniaturization without sacrificing reliability.
Material Definition, Molecular Structure, and Key Characteristics
Ultem (PEI) Material Definition
Ultem, the trade name for Polyetherimide (PEI), is a high-performance amorphous thermoplastic known for its exceptional thermal stability, inherent flame retardancy, and dimensional precision. Unlike semicrystalline polymers such as PEEK or PPS, Ultem’s amorphous molecular structure ensures uniform shrinkage, minimal warpage, and optical clarity.
A defining feature of Ultem is its intrinsic flame resistance—it achieves UL94 V-0 ratings without the use of additives or halogen-based compounds, a major advantage in aerospace, electronics, and medical sectors that require low smoke and low toxicity (FST compliance).
With a glass transition temperature (Tg) of approximately 217°C, Ultem maintains mechanical integrity and stiffness at temperatures where most engineering plastics soften or deform. This makes it one of the few materials suitable for continuous operation above 170°C while retaining both electrical insulation and mechanical performance.
Molecular Structure and Why Ultem Has Exceptional Heat Resistance
Ultem’s outstanding thermal endurance originates from its aromatic polyimide backbone. The aromatic rings impart rigidity and thermal stability by restricting molecular motion, while the ether linkages (-O-) between repeating units provide a controlled degree of flexibility, preventing brittleness. The imide groups (-CO–NH–CO-) contribute to high strength and chemical resistance through strong intermolecular bonding.
These structural features give Ultem a unique combination of:
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High heat deflection temperature (HDT ~200°C)
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Excellent strength retention at elevated temperatures
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Minimal creep deformation under load
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Outstanding dielectric properties even in humid or hot environments
Because Ultem is amorphous, it does not have a distinct melting point—allowing it to maintain dimensional stability and optical uniformity across thermal cycles, unlike semicrystalline polymers which undergo expansion or shrinkage transitions.
Ultem vs Other High-Temperature Polymers (PEEK / PSU / PES)
| Property / Feature | Ultem (PEI) | PEEK | PSU / PES |
| Structure Type | Amorphous | Semi-crystalline | Amorphous |
| Tg (°C) | 217 | 143 | 190 |
| Continuous Use Temp (°C) | 170 | 250 | 160 |
| Flame Retardancy | Inherent V-0 | Additive required | Inherent V-0 |
| Smoke / Toxicity | Very low (FST compliant) | Moderate | Moderate |
| Machinability | Excellent | Difficult | Good |
| Transparency | Amber-transparent | Opaque | Amber-transparent |
Engineering Insight:
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Ultem (PEI) offers the best balance between processability, heat resistance, and regulatory safety, making it ideal for aerospace interiors, medical housings, and electrical insulators.
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PEEK outperforms in chemical and mechanical endurance, but at a higher cost and processing complexity.
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PSU and PES provide similar thermal profiles but with lower strength and FST performance compared to Ultem.
In short, Ultem’s aromatic, flame-retardant, amorphous polymer structure explains why it remains the material of choice when components must combine heat resistance, dimensional accuracy, and safety compliance in critical engineering environments.
Material Properties: Mechanical, Thermal, Electrical, and Chemical Behavior
Mechanical Properties
Ultem (PEI) combines high strength, stiffness, and creep resistance, making it one of the most dimensionally stable amorphous thermoplastics available. Its tensile strength typically ranges from 100–110 MPa, while its flexural modulus reaches 3.2–3.5 GPa, maintaining mechanical integrity even at elevated temperatures above 150°C.
Unlike most engineering plastics, Ultem demonstrates minimal creep deformation under constant load, an essential property for structural components in aerospace, electrical, and industrial assemblies that experience long-term mechanical stress.
Impact strength is moderate—higher than acrylics and polyesters but lower than polycarbonate or PEEK. When reinforced with glass fibers (typically 30%), the modulus can double (up to 6.5 GPa), significantly improving rigidity, load-bearing capability, and dimensional precision. This glass-filled Ultem is widely used in mechanical housings, fixtures, and heat-resistant support structures.
Thermal Properties
One of Ultem’s defining advantages lies in its exceptional heat resistance. The glass transition temperature (Tg) is approximately 217°C, far higher than most engineering plastics such as PC (~147°C) or PPSU (~190°C). Its heat deflection temperature (HDT) can exceed 200°C under 1.8 MPa load, allowing continuous use around 170°C without distortion.
The thermal oxidation stability of Ultem is excellent due to its aromatic imide structure, which resists chain scission under heat and oxygen exposure. The thermal decomposition temperature exceeds 500°C, giving a wide safe processing and operational window.
Another notable property is its low coefficient of thermal expansion (CTE)—about 5×10⁻⁵ /°C—which ensures dimensional accuracy even across large temperature swings. Furthermore, Ultem achieves UL94 V-0 flame retardancy inherently, without halogen additives, because its aromatic backbone and imide linkages form a carbonaceous char layer during combustion, limiting oxygen penetration and flame propagation.
Electrical & Chemical Resistance
Ultem excels in electrical performance, offering high dielectric strength (≈16–20 kV/mm), low dielectric constant (~3.1 at 1 MHz), and excellent insulation retention even at elevated temperatures and humidity levels. This makes it a prime choice for connectors, insulating supports, and electrical housings in demanding environments.
Chemically, Ultem provides strong resistance to acids, alcohols, and aqueous solutions, while maintaining moderate resistance to hydrocarbons and oils. However, it is partially soluble in chlorinated or aromatic solvents like methylene chloride, so exposure to these should be minimized.
A standout feature is Ultem’s hydrolytic stability—it can withstand thousands of autoclave sterilization cycles (121–134°C steam) without mechanical degradation or stress cracking. This makes it one of the few thermoplastics approved for repeated-use medical devices, dental instruments, and sterilizable enclosures.
In summary, Ultem’s mechanical strength, high Tg, flame retardancy, dielectric performance, and hydrolysis resistance make it uniquely suited for aerospace, electronic, and medical-grade engineering applications where long-term dimensional stability and reliability are critical.
Ultem Grades: Ultem 1000, Ultem 9085, and Specialty PEI Variants
Ultem 1000
Ultem 1000 is the unfilled, natural-grade Polyetherimide (PEI)—the baseline formulation from which most other Ultem variants are derived. It features high toughness, excellent dimensional stability, and outstanding dielectric strength, making it the preferred choice for precision-machined components, electrical insulators, and analytical equipment parts.
Its amorphous structure provides uniform shrinkage and low internal stress, essential for tight-tolerance CNC machining and injection-molded housings that must maintain accuracy across temperature variations. With continuous service temperature up to 170°C, Ultem 1000 is also a popular choice in semiconductor handling tools and medical enclosures that demand long-term dimensional reliability.
Ultem 9085
Ultem 9085 is a high-performance aerospace-certified PEI blend known for its exceptional FST (Flame, Smoke, Toxicity) compliance—a requirement for interior aircraft applications under FAR 25.853 regulations. It combines the heat resistance and rigidity of Ultem 1000 with enhanced toughness and processability, especially in additive manufacturing (FDM 3D printing).
Key properties include:
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UL94 V-0 flame rating
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Low smoke emission and toxicity
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Excellent strength-to-weight ratio
Because of these traits, Ultem 9085 is widely used in aircraft panels, ducts, brackets, and seat assemblies, where lightweight structure, safety certification, and durability are critical. Its consistent mechanical performance across 3D-printed layers also makes it a top choice for rapid prototyping and end-use aerospace components.
Ultem 1000 vs Ultem 9085 — The Key Difference
Two primary commercial grades dominate industrial use:
| Grade | Description | Key Applications |
| Ultem 1000 | Unfilled PEI resin; highest strength and rigidity | Machined components, insulators, semiconductor fixtures |
| Ultem 9085 | PEI + carbon blend; FST-rated and FAA-certified | Aerospace interior panels, 3D printed parts, aircraft brackets |
Ultem 9085, in particular, is certified for aerospace use due to its FST (Flame, Smoke, Toxicity) compliance, making it a preferred choice for 3D printing and lightweight aircraft assemblies. Ultem 1000, on the other hand, remains the benchmark for precision-machined parts requiring excellent mechanical and dielectric stability.
Other Common Ultem Grades
| Grade | Reinforcement / Property | Typical Applications |
| Ultem 2300 | 30% Glass-Filled | Structural components, fixtures, connectors — improved stiffness and creep resistance |
| Ultem 1010 | High-strength FDM printable PEI | Medical and food-contact parts — FDA and NSF certified |
| Ultem 3451 / 3452 | High-flow injection molding grade | Thin-wall electrical and automotive housings |
| Ultem CRS / Chemical-Resistant Series | Modified PEI for solvent exposure | Fuel system parts, chemical process components |
Engineering Insight: Each Ultem variant is optimized for a specific balance between mechanical performance, processing ease, and regulatory compliance.
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Ultem 1000 → precision machining, dielectric stability
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Ultem 2300 → mechanical rigidity and structural reliability
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Ultem 9085 → aerospace-certified lightweight safety performance
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Ultem 1010 → sterilizable medical and food-grade systems
In design selection, reinforcement, flame retardancy, and regulatory approvals should guide material choice rather than just mechanical properties.
Manufacturing Ultem: CNC Machining, Injection Molding, and Additive Manufacturing
CNC Machining Ultem
Ultem (PEI) is highly machinable but requires precise process control due to its high rigidity, low thermal conductivity, and sensitivity to residual stress. Its stiffness contributes to accelerated tool wear, particularly at cutting edges during prolonged operations. Using carbide or diamond-coated tools is recommended to maintain surface quality and dimensional consistency.
A key challenge is heat accumulation—Ultem’s low thermal conductivity causes localized heating, which can lead to surface whitening or microcracking. To mitigate this, stepwise machining (rough + finish passes) and air or nitrogen cooling should be used instead of flood coolant, which can introduce moisture or stress.
Warping control is another critical factor. Ultem tends to relieve internal stress during cutting, causing slight deformation in large or thin-walled parts. Engineers typically use pre-annealed stock and balanced machining strategies (alternating side cuts) to preserve flatness and precision. For tight-tolerance components, final finishing should be done after thermal stress relief to stabilize geometry.
Injection Molding Guidelines
Ultem requires a strictly controlled molding environment, as moisture contamination can cause bubbles, silver streaks, or molecular degradation.
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Drying condition: 150°C for 3–4 hours (moisture < 0.02%)
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Melt temperature: 340–400°C
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Mold temperature: 170–200°C (to ensure molecular relaxation and dimensional stability)
Because Ultem is amorphous, it exhibits uniform shrinkage (≈0.5–0.7%), minimizing warpage but requiring careful cooling rate control to avoid internal stress. High injection pressures and proper gate positioning are essential to ensure complete cavity filling in thin-wall or high-precision parts.
Gating and cooling design must consider its high viscosity and low flowability; rounded runners, generous gates, and uniform mold temperature help maintain part clarity and structural integrity. Sudden cooling can cause residual stress and optical haze, especially in transparent or thin components.
Ultem for 3D Printing (Ultem 9085 / 1010)
Additive manufacturing has expanded Ultem’s use beyond traditional molding. Ultem 9085 and Ultem 1010 are the leading PEI filaments approved for aerospace, medical, and industrial-grade FDM (Fused Deposition Modeling).
Both materials require heated chambers (≥170°C) to prevent delamination and maintain strong interlayer adhesion.
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Ultem 9085: Certified for aerospace FST compliance, ideal for ducts, brackets, and cabin panels.
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Ultem 1010: Offers higher tensile strength and biocompatibility, used in medical tools and sterilizable components.
Proper control of bed temperature, chamber environment, and cooling rate is vital to achieve isotropic strength. When processed correctly, printed Ultem parts can match or exceed 70–80% of injection-molded mechanical strength, providing lightweight, high-performance alternatives for functional prototypes or end-use parts.
Engineering Summary:
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CNC machining demands thermal control and stress management.
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Injection molding requires precise drying and temperature stability.
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3D printing of Ultem (9085/1010) enables aerospace-grade lightweight manufacturing.
Together, these processes make Ultem one of the few polymer families bridging precision machining, high-temperature molding, and certified additive manufacturing.
Common Failure Modes and Engineering Solutions for Ultem
Stress Cracking and Brittleness at High Load
Ultem’s high stiffness, while advantageous for dimensional accuracy, can make it susceptible to brittle failure under high localized stress or impact, especially around sharp corners, thin sections, or molded-in stress zones. The most common cause of cracking is stress concentration from design geometry, machining marks, or improper gating in molded parts.
Engineering Solutions:
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Introduce fillets or chamfers at all internal corners to reduce stress concentration.
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Maintain uniform wall thickness to avoid local cooling stress.
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For injection molding, use lower Melt Flow Rate (MFR) grades to reduce brittleness and improve impact resistance.
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Consider annealing post-processing to relieve internal stress in machined or molded components.
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Avoid solvent exposure during cleaning or bonding, as PEI can develop microcracks in stressed zones.
Thermal Oxidation and Discoloration
When exposed to temperatures above 150°C for extended periods, Ultem gradually undergoes thermal oxidation, especially in oxygen-rich environments. This process leads to molecular chain scission, resulting in embrittlement, surface cracking, and color changes—typically from amber to dark brown.
Discoloration is a visual indicator of surface oxidation, but mechanical degradation usually precedes visible color shift. Continuous exposure to heat accelerates this process, particularly if the part experiences repeated heating and cooling cycles.
Engineering Solutions:
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Maintain operating temperature below 170°C continuous or 200°C intermittent.
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Use stabilized Ultem grades with enhanced oxidative resistance (e.g., aerospace or electrical variants).
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For long-life parts, design with ventilation or reflective coatings to reduce heat buildup.
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Avoid unnecessary regrind use during molding, as recycled material oxidizes faster.
Injection Molding Defects
Due to Ultem’s narrow processing window (370–400°C melt temperature), improper molding parameters often cause defects that impact mechanical and optical quality.
Common Defects:
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Jetting and silver streaks: Result from moisture contamination or high injection velocity.
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Burn marks: Caused by trapped air and excessive shear heating near gates.
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Voids: Occur due to insufficient packing or non-uniform cooling, particularly in thick-wall parts.
Engineering Solutions:
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Dry material thoroughly (150°C × 3–4 h, moisture <0.02%).
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Use balanced gating systems and slow initial injection speeds to prevent jetting.
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Optimize packing pressure and cooling uniformity to eliminate voids.
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Maintain proper venting and control residence time to prevent overheating and degradation.
Summary Insight: Most Ultem failures originate from thermal stress, residual molding stress, or chemical oxidation rather than inherent material weakness. Proper design geometry, controlled molding parameters, and post-processing (annealing, stabilization) are key to maintaining mechanical integrity and long-term performance in high-reliability Ultem components.
Ultem vs PEEK vs G10 — Engineering Material Selection Guide
Ultem vs PEEK
Both Ultem (PEI) and PEEK (Polyether Ether Ketone) belong to the high-performance polymer family, but they occupy different positions in terms of cost, thermal capability, and manufacturability.
Thermal Performance: PEEK offers superior heat resistance, with continuous use temperatures up to 260°C, compared to Ultem’s 170°C. However, Ultem maintains excellent thermal stability for most aerospace and electronic applications where extreme heat is not sustained.
Mechanical Behavior: PEEK has higher fatigue strength and toughness, making it suitable for high-stress, load-bearing components such as gears and structural mounts. Ultem, on the other hand, provides excellent rigidity, low creep, and dimensional accuracy, ideal for precision enclosures, insulators, and lightweight assemblies.
Cost and Manufacturability: Ultem is 40–50% more cost-effective than PEEK and offers easier injection molding due to its amorphous nature. For high-volume production or weight-sensitive parts, Ultem is often preferred, whereas PEEK is chosen when ultimate mechanical endurance and chemical resistance are mandatory.
| Property | Ultem (PEI) | PEEK |
| Continuous Use Temp | 170°C | 260°C |
| Tensile Strength | ~110 MPa | ~120 MPa |
| Processability | Excellent (amorphous) | More challenging (semi-crystalline) |
| Cost | Moderate | High |
| Key Advantage | Cost-effective high performance | Extreme mechanical & thermal endurance |
Ultem vs G10 (FR4)
G10, also known as FR4, is a glass-reinforced epoxy laminate, whereas Ultem is a thermoplastic polymer. Despite both offering excellent electrical insulation, their processing methods and mechanical behavior differ dramatically.
Mechanical & Processing Differences:
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G10 exhibits very high stiffness and compressive strength, but is brittle and non-formable.
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Ultem offers impact resistance and flexibility, allowing injection molding, CNC machining, and 3D printing for complex geometries.
Electrical Properties: Both materials have high dielectric strength, but Ultem maintains this property over a wider temperature range, making it more suitable for high-temperature insulators and electronic housings where G10 would degrade or delaminate.
| Property | Ultem (PEI) | G10 / FR4 |
| Structure | Amorphous thermoplastic | Glass-epoxy laminate |
| Machinability | High (moldable, CNC) | Limited (machining only) |
| Electrical Insulation | Excellent (wide temp range) | Excellent (room temp) |
| Impact Strength | High | Low (brittle) |
| Applications | Housings, insulators, aerospace | PCBs, circuit supports |
Which Material Should You Choose?
By Engineering Application:
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Aerospace Lightweight Structures: Ultem 9085 — certified FST compliance, 3D-printable.
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Medical and Sterilizable Components: Ultem 1000 — strong hydrolysis resistance, repeat autoclaving.
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Heavy-Duty Structural or Wear Components: PEEK — superior fatigue resistance and chemical durability.
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Electrical Insulation Boards and Circuit Substrates: G10 / FR4 — unmatched stiffness and dielectric stability.
Summary Insight:
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Choose Ultem for cost-effective, high-temperature precision parts.
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Choose PEEK for maximum mechanical and chemical endurance.
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Choose G10 for flat, high-stiffness electrical insulation panels.
In modern engineering design, Ultem stands as the optimal middle ground between PEEK’s performance and G10’s cost efficiency, offering an ideal balance of processability, strength, and safety compliance across aerospace, medical, and industrial sectors.
Industrial Applications of Ultem (PEI)
Aerospace Components
Ultem (PEI) is widely recognized as one of the few thermoplastics approved under FAR 25.853 for flame, smoke, and toxicity (FST) compliance — a critical requirement for aircraft interior and structural materials. Its combination of lightweight performance, inherent flame resistance, and dimensional stability makes it a preferred alternative to aluminum and thermoset composites.
Typical Aerospace Applications:
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Interior panels, ducts, and seating components — maintaining structural integrity at high cabin temperatures.
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Electrical and pneumatic connectors — leveraging Ultem’s superior insulation and dielectric stability.
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Support brackets and structural mounts — benefiting from high rigidity and low creep under sustained load.
Ultem 9085 and Ultem 1000 grades are extensively used in aerospace additive manufacturing, enabling FDM-printed lightweight parts with certified material traceability and mechanical reliability.
Medical Devices
In medical engineering, Ultem (PEI) offers a unique combination of biocompatibility, sterilization endurance, and mechanical strength, making it suitable for both reusable and semi-disposable instruments. Unlike many high-temperature plastics, Ultem can withstand repeated autoclave sterilization (134°C steam) without property degradation or discoloration.
Common Medical Applications:
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Surgical and dental instruments — requiring high stiffness and sterilization compatibility.
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Electronic housings and diagnostic equipment covers — combining dielectric strength with chemical resistance to disinfectants.
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Insulating and mounting components — maintaining dimensional precision even after multiple sterilization cycles.
Ultem 1000 and medical-grade PEI variants comply with ISO 10993 and USP Class VI standards, ensuring safe contact with biological systems and long-term reliability in medical environments.
Electronics & High-Temperature Enclosures
Ultem’s excellent dielectric strength (≈20 kV/mm) and thermal endurance up to 200°C make it a core material in electronic insulation, connector housings, and sensor enclosures where stability under heat and voltage stress is crucial. Its low moisture absorption and hydrolytic stability ensure consistent electrical performance even in humid or chemically active environments.
Typical Electrical and Industrial Applications:
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High-temperature connectors and circuit housings for automotive and aerospace electronics.
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Thermal barrier insulators and switch components operating near engines or power modules.
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Precision coil forms, relays, and sensor casings requiring both dimensional stability and long service life.
Engineering Insight: Across aerospace, medical, and electronic sectors, Ultem delivers a rare balance of thermal resistance, flame safety, electrical insulation, and structural rigidity. It remains one of the most trusted high-performance polymers for applications demanding lightweight reliability under extreme environments.
Design for Manufacturability (DFM) for Ultem Components
Wall Thickness & Geometry
Ultem (PEI) has excellent rigidity but relatively low ductility compared to semi-crystalline polymers, which means design geometry directly affects part strength and stress distribution. Uneven wall thickness and sharp transitions are the main causes of warpage and stress cracking in injection-molded or machined Ultem parts.
Key DFM Guidelines:
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Maintain uniform wall thickness (typically 1.5–4.0 mm) to ensure even cooling and reduce internal stress.
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Avoid abrupt cross-sectional changes; use smooth fillets (≥1.5× wall thickness) to minimize localized stress.
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Reinforce large flat areas with ribs or gussets instead of increasing wall thickness, which can lead to sink marks and internal voids.
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For load-bearing parts, consider using glass-filled Ultem grades (e.g., Ultem 2300) to improve stiffness and reduce deformation under load.
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In complex geometries, incorporate draft angles of 1–2° to enable easier demolding and reduce stress at ejection points.
Example: A 3 mm-thick Ultem housing wall with uniform rib reinforcement will cool evenly and retain dimensional precision better than a 5 mm-thick section with no ribs.
Tolerance and Dimensional Stability
Due to its amorphous molecular structure, Ultem exhibits very low shrinkage (≈0.5%) and high dimensional repeatability, making it ideal for precision components. However, its high thermal expansion coefficient (~5×10⁻⁵ /°C) must be considered during both machining and injection molding.
Recommended Tolerances:
| Manufacturing Method | Typical Tolerance | Notes |
| CNC Machining | ±0.02–0.05 mm | Requires stable fixturing; avoid heat buildup. |
| Injection Molding | ±0.05–0.10 mm | Shrinkage compensation required for thick walls. |
| 3D Printing (FDM) | ±0.15–0.25 mm | Depends on printer accuracy and thermal control. |
Engineering Considerations:
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For CNC components, always machine under controlled temperature to minimize dimensional drift.
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Avoid tight fits in assemblies exposed to wide thermal ranges; use floating joints or expansion clearances.
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Post-molding annealing can further improve dimensional stability and stress relaxation for precision parts.
Surface Finishing Options
Ultem’s surface can be finished, textured, or polished depending on functional and aesthetic requirements. Its high glass transition temperature allows for various finishing techniques without losing dimensional integrity.
Common Finishing Techniques:
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Polishing: Mechanical or buff polishing achieves optical-grade clarity for transparent Ultem parts (used in lenses, windows, and housings).
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Bead Blasting: Provides uniform matte or anti-glare finishes while maintaining dimensional accuracy — ideal for enclosures and covers.
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Vapor Smoothing: Applied primarily to FDM 3D-printed Ultem parts (Ultem 9085/1010) to enhance surface uniformity and reduce layer visibility without altering tolerances.
Additional Notes: Avoid aggressive chemical polishing agents — Ultem is sensitive to solvents like acetone and alcohol, which can induce stress cracking. Always ensure surfaces are fully dried and stress-relieved before finishing for optimal longevity.
Summary Insight: A well-designed Ultem component balances wall uniformity, controlled tolerances, and appropriate finishing to achieve both performance and aesthetics. By accounting for thermal expansion, stress concentration, and post-processing, engineers can fully leverage Ultem’s unique combination of precision, strength, and high-temperature capability.
Summary
Ultem (PEI) is a high-performance engineering plastic that is valued for its ability to resist heat, its natural flame resistance, and its excellent dimensional stability. It can be used continuously at temperatures up to 170 °C and has UL94 V-0 flame ratings. It stays accurate during molding, machining, and 3D printing. Ultem 1000 (unfilled, high toughness) and Ultem 9085 (aerospace-certified, FST compliant) are two important grades that offer customized performance for a wide range of uses, from medical devices to lightweight aerospace parts.
Ultem is a cost-effective alternative to ultra-high-performance polymers like PEEK because it has good electrical insulation, is resistant to impact, and can be made reliably. When dried and processed correctly, it makes parts for aerospace interiors, electronic housings, and high-temperature structural components that are strong, safe, and stable in size. This gives engineers a flexible and reliable material for tough environments.
FAQ
What is Ultem plastic used for?
Ultem (PEI) is used in aerospace interiors, electrical housings, medical devices, and high-temperature enclosures due to its heat resistance, strength, and flame retardancy.
Is Ultem stronger than PEEK?
Not in tensile strength or fatigue life — PEEK is stronger and more fatigue-resistant, while Ultem is more cost-effective and easier to mold.
What is the melting point of Ultem?
Ultem’s glass transition temperature (Tg) is around 217°C, and it begins softening above 230°C, making it ideal for continuous use up to 170°C.
Is Ultem safe for food or medical use?
Yes. Ultem 1000 and medical-grade PEI meet FDA, ISO 10993, and USP Class VI standards, allowing safe use in food-contact and sterilizable medical components.
Can Ultem be CNC machined?
Yes. Ultem can be precisely CNC machined with carbide or PCD tools, but heat buildup must be minimized to avoid whitening or warping.
Can Ultem withstand autoclave sterilization?
Yes. Ultem withstands repeated steam sterilization at 134°C without losing mechanical or electrical properties — ideal for reusable surgical instruments.
What is the difference between Ultem 1000 and Ultem 9085?
Ultem 1000: Unfilled, high toughness, excellent for CNC and precision parts.
Ultem 9085: Aerospace-grade with certified flame/smoke/toxicity (FST) performance, optimized for 3D printing and lightweight components.
What materials are alternatives to Ultem?
Common alternatives include:
PEEK — higher temperature and chemical resistance.
PPSU / PSU — better hydrolytic stability.
G10 (FR4) — higher stiffness but limited machinability. Each is selected based on performance, cost, and processing method.
About the Author: Gavin Xia
This article was written by engineers from the RAPID PROTOS team. Gavin Xia is a professional engineer and technical expert with 20 years of experience in rapid prototyping, metal parts, and plastic parts manufacturing.
