PEI plastic

PEI plastic is an amorphous high-performance thermoplastic that combines high stiffness, good dimensional stability, electrical insulation and pronounced heat resistance. Polyetherimide is therefore used for technical components that must function reliably over a wide temperature range while also meeting tight tolerances, low creep tendency or requirements for fire behaviour.

Martan Plastics supplies suitable plastic semi-finished products made of PEI and manufactures precise components from them to drawing, sample or CAD data. As part of plastic machining, individual parts, prototypes, small series and recurring series parts can be produced to suit the application.

What is PEI plastic?

PEI is the short name for polyetherimide. The material belongs to the group of amorphous high-performance plastics. Unlike semi-crystalline thermoplastics, PEI does not have a clearly defined melting point. As temperature rises, the material softens gradually. The glass transition temperature is therefore an important characteristic. For common unreinforced PEI types it is approximately 217 °C.

The amorphous structure enables low and comparatively uniform processing shrinkage. This supports dimensionally accurate geometries and tight tolerances. Natural-coloured PEI is typically transparent amber. Coloured, glass-fibre-reinforced and grades designed for special regulatory requirements can differ significantly from this.

In the market, PEI is often associated with the brand name ULTEM™. However, ULTEM is a material family or trade name. For technical selection, the specific PEI type, its reinforcement, approvals and the associated data sheet are therefore always decisive.

PEI properties at a glance

The following details serve to classify the material. Reliable limit values are derived exclusively from the data sheet of the intended PEI grade and from the real operating conditions. Temperature, load duration, stress, component thickness, notches, media contact, moisture and manufacturing process influence the actual suitability.

Property	Typical classification	Significance for the application
Material structure	amorphous	Uniform shrinkage and good conditions for dimensionally accurate components
Density	unreinforced approx. 1.27 to 1.28 g/cm³	Weight advantage over many metals
Glass transition temperature	approx. 217 °C for standard types	High thermal performance, but no blanket continuous service approval
Mechanics	high strength and stiffness	Suitable for loaded housings, supports, insulators and precision parts
Electrical properties	high dielectric strength, good insulation	Interesting for electrical and electronic components
Fire behaviour	inherently flame-retardant, low smoke development with suitable types	Advantageous in transport engineering, electronics and aviation; check the specific standard
Water absorption	lower than many polyamides, but not zero	Consider moisture in tolerances, drying and electrical characteristics
Chemical resistance	good against many oils, fuels, alcohols and diluted media	Not universal; stress cracking possible with certain solvents
Colour	natural usually transparent amber	Visual inspection and transparent technical components possible

High temperature resistance and dimensional stability

PEI retains strength and stiffness at elevated temperatures significantly better than many standard and engineering plastics. For permanently loaded components, however, the glass transition temperature alone must not be used as the argument. The permissible service temperature depends on material type, load level, duration of use and safety requirements.

For precision components, in addition to nominal temperature resistance, the heat deflection temperature of plastics must be assessed in particular. Thanks to its amorphous structure and low shrinkage, PEI offers good conditions for tight tolerances. Under high mechanical loads, creep and stress relaxation nevertheless remain relevant to the design.

Mechanical strength and stiffness

Unreinforced PEI has high strength and stiffness. Glass-fibre-reinforced types increase the modulus of elasticity, dimensional stability and load capacity in particular. However, they can cause anisotropic behaviour, greater tool wear and more brittle notch sensitivity.

Reinforcement is therefore not automatically the better choice. For complex contours, snap hooks or impact-loaded areas, an unreinforced or toughened modified type may be more suitable.

Electrical insulation and fire behaviour

PEI has good dielectric properties and is used for insulators, connectors, coil formers, switch components and housings. This combination is particularly relevant for plastics in the electrical industry and for plastics in electronics.

Many PEI grades are inherently flame-retardant without additional halogen-containing flame retardants and show comparatively low smoke development. Whether a specific UL, rail, aviation or smoke gas toxicity requirement is met must, however, be verified on the basis of the exact material type, component thickness and test standard.

Hydrolysis and radiation resistance

PEI shows good resistance to hot water and repeated steam exposure. This makes the material interesting for selected components that can be sterilised repeatedly. However, the number of permissible cycles depends on temperature, pressure, cleaning chemistry, mechanical stress and material type.

Depending on the grade, PEI also has good resistance to ionising radiation. For applications in medical technology, testing technology or radiation-exposed environments, dosage, atmosphere and the required residual characteristics must be taken into account.

Chemical resistance: good, but not universal

PEI is resistant to numerous hydrocarbons, fuels, oils, alcohols and diluted aqueous media. However, certain ketones, chlorinated solvents, strong bases and other stress-cracking agents can be critical.

A material can remain unremarkable in unloaded laboratory contact and still crack under internal or external stress. For safety-relevant applications, a media test on the intended PEI type under realistic temperatures, exposure times and mechanical loads is therefore recommended. Cleaning agents, assembly aids, adhesives and cooling lubricants should also be included in this assessment.

Advantages of PEI plastic

• High thermal load capacity combined with high stiffness
• Good dimensional stability and comparatively low processing shrinkage
• Very good electrical insulation properties
• Inherently flame-retardant behaviour with many material types
• Low smoke development for selected transport engineering and aviation applications
• Good hydrolysis resistance and suitability for selected sterilisation processes
• Natural-coloured transparent amber version available
• Machinable as sheet, rod and other semi-finished product
• Available for injection moulding, extrusion and additive manufacturing
• Glass-fibre-reinforced and application-specific modified grades available

Limits and disadvantages of PEI

• Higher price level than standard plastics and many engineering thermoplastics
• Lower chemical resistance than PEEK or PTFE against particularly aggressive media
• Sensitivity to certain solvents and stress cracking
• Notches, sharp corners and introduced stresses can reduce component safety
• Moisture absorption is low, but must not be ignored in precision and processing
• High processing temperatures and careful material drying required
• Glass-fibre-reinforced types can cause direction-dependent properties and higher tool wear
• For heavy continuous sliding and wear stress, specially modified materials are often better suited

PEI semi-finished products and material types

PEI is available as sheet, rod, profile, granulate and filament. For machined finished parts, PEI semi-finished products form the economical starting basis. Which dimensions and grades are available depends on the manufacturer and the specific project.

PEI type	Typical thickness	Suitable tasks
Unreinforced PEI	balanced strength, electrical properties, amber transparency	Insulators, housings, test fixtures, precision parts
PEI GF30	higher stiffness, lower thermal expansion, improved dimensional stability	Structural parts, supports, loaded housings and holders
Flow-optimised PEI types	better mould filling for thin or complex injection-moulded parts	Connectors, thin-walled components, series parts
PEI for additive manufacturing	adapted flow and fire behaviour depending on filament type	Prototypes, fixtures, small series, complex channels
Regulatorily specified PEI types	material-dependent approvals for aviation, food or medical	Components with documentation and approval-relevant requirements

Typical applications of PEI plastic

Electrical engineering and electronics

PEI is used for electrical insulating parts, connectors, coil formers, switch components, sensor carriers and thermally loaded housings. The material combines electrical insulation with temperature resistance and dimensional stability.

For high voltage, high frequency or safety-relevant components, creepage distances, dielectric strength, moisture and the specific test standard must be assessed together.

Semiconductor technology and cleanroom applications

In the semiconductor industry, PEI can be used for test adapters, carriers, insulators, handling components and parts in thermally loaded systems.

For cleanroom applications, particle behaviour, outgassing, cleanability, ionic contamination and the specific material batch must be checked. A general classification of the polymer is not sufficient for critical process environments.

Aerospace

For plastic components in aerospace, PEI is interesting because of its favourable ratio of weight, stiffness, fire behaviour and smoke development.

Typical fields of use are interior components, holders, cable and electronic components as well as selected structural and functional components. The specific material approval, traceability and the applicable test requirements are always decisive.

Mechanical and plant engineering

In mechanical and plant engineering, PEI is suitable for example for insulating plates, guides, fixtures, test devices, housings, spacers and components in thermally loaded assemblies.

The material can replace metal when weight reduction, electrical insulation or freedom from corrosion are the priority. For highly loaded threads, localised compression and continuous wear, however, the design must be matched to the properties of the plastic.

Medical technology and sterilisation

Selected PEI grades can be considered for repeatedly sterilisable instrument components, handles, holders and housings. Material approval, biocompatibility, cleaning chemistry and the actual number of sterilisation cycles must be checked separately.

PEI is not automatically approved for medical applications simply because of its polymer designation.

Machining and processing PEI

Milling, turning and drilling PEI

PEI can be machined from sheets and rods. Typical processes are milling, drilling, sawing and CNC turning. For precise components, sharp tools, controlled heat generation and low-stress clamping are important.

Excessive heat input can cause local deformation or dimensional deviations. With glass-fibre-reinforced PEI, tool wear also increases. Thin walls and delicate contours should be clamped in such a way that no permanent stresses are introduced into the component.

For tight tolerances, machining in several steps can be useful. The component can relax between roughing and finishing. This allows dimensional changes after the final machining step to be reduced.

The suitable parameters within CNC plastic machining depend on the semi-finished product, reinforcement, component geometry and required surface quality.

Designing PEI components

PEI should be designed in a way that is appropriate for plastics. Metal designs cannot always be transferred unchanged to the material. The following must be observed in particular:

• Sufficient radii instead of sharp internal corners
• Uniform wall thicknesses for injection-moulded parts
• Avoidance of unnecessarily high notch stresses
• Sufficient areas for screws, bushes and inserts
• Consideration of thermal expansion and creep behaviour
• Load distribution instead of localised overloading
• Tolerances that match the manufacturing process and service temperature range

Threads can be cut directly into PEI. For frequent assembly operations or high tightening torques, threaded inserts may be more sensible. The decision depends on wall thickness, temperature, load cycles and quantity.

Injection moulding, extrusion and 3D printing

PEI can be processed into complex series parts in injection moulding. Because of the high processing temperatures, suitable machines, tools and careful drying are required. Moisture can lead to hydrolysis, surface defects and a drop in mechanical properties.

For profiles and certain semi-finished product geometries, extrusion is an option.

In additive manufacturing, PEI is used above all for functional prototypes, fixtures and small series. The process requires high nozzle, chamber and build plate temperatures. Design, layer adhesion and anisotropy must be taken into account in the layout.

PEI compared with other high-performance plastics

A further introduction to material selection is provided by the overview of high-performance plastics and the comparison of PEEK, PPS and PSU.

The final selection should not be based on a single peak value, but on the complete specification.

Material	Structure	Strength compared with PEI	Weakness compared with PEI	Typical selection question
PEEK	semi-crystalline	higher chemical, wear and continuous temperature resistance	usually significantly higher price level; not transparent	Are extreme media, friction or temperatures decisive?
PPS	semi-crystalline	very good chemical resistance and low water absorption	often more brittle; different dimensional and processing characteristics	Does chemical resistance take priority over transparency and toughness?
PPSU	amorphous	very high impact strength and good repeated sterilisation capability	lower stiffness and thermal performance	Are impact load and sterilisation cycles more important?
PSU	amorphous	economical alternative for moderate requirements	lower temperature resistance and strength	Is a lower performance level sufficient?
PES/PESU	amorphous	good hydrolysis and heat resistance	property profile and availability differ by type	Which combination of toughness, chemistry and temperature is required?
PI	mostly not melt-processable	higher thermal limit performance and low creep tendency	more expensive and more demanding in production and machining	Is the application above the sensible PEI range?

When is PEI the right plastic?

PEI is particularly interesting when several of the following requirements must be met at the same time:

• Permanently elevated temperatures with high stiffness
• Electrical insulation over a wide temperature range
• Good dimensional stability and low shrinkage
• Inherently flame-retardant behaviour and low smoke development
• Good hydrolysis resistance or repeated steam exposure
• Weight reduction compared with metal
• Complex geometries in injection moulding or precise machining from semi-finished product
• Amber transparency for visual or inspection functions

PEI should, however, be critically assessed if the component is permanently in contact with aggressive solvents, experiences extreme wear or sliding stress, requires very high impact strength or is operated above the temperature range permissible for the specific PEI type.

Information for the selection and manufacture of PEI components

The more precisely the operating conditions are described, the more reliably the material type, semi-finished product and manufacturing process can be selected. The following details are particularly helpful for a technical enquiry:

• Component drawing, CAD data or meaningful sample
• Dimensions, tolerances and required surface quality
• Continuous and peak temperature including load condition
• Mechanical forces, pressure, tension, bending, impact and vibration
• Media contact with concentration, temperature and exposure time
• Electrical requirements and relevant test voltages
• Fire, smoke, food, medical or aviation requirements
• Sterilisation and cleaning processes including number of cycles
• Need for unreinforced, glass-fibre-reinforced or coloured PEI
• Quantity, repeat requirement and desired documentation

Martan Plastics supports material selection and manufactures technical plastic products as semi-finished product, cut piece or precise finished part. This allows clarification at an early stage whether PEI meets the requirements or whether another high-performance plastic is more sensible technically and economically.

PEI ULTEM® in different glass-fibre reinforcements

For applications with high requirements for temperature resistance, strength and dimensional stability, various PEI materials based on ULTEM® are available. The range includes PEI NATURELL ULTEM® 1000-1000 as well as the black version PEI SCHWARZ ULTEM® 1000-7101. For higher mechanical load capacity, glass-fibre-reinforced variants are available, including PEI GV10% NATURELL ULTEM® 2100-1000, PEI GV20% NATURELL ULTEM® 2200-1000 and PEI GV20% SCHWARZ ULTEM® 2200-7301. For even higher requirements, PEI GV30% NATURELL ULTEM® 2300-1000, PEI GV30% SCHWARZ ULTEM® 2300-7301, PEI GV40% NATURELL ULTEM® 2400-1000 and PEI GV40% SCHWARZ ULTEM® 2400-7301 can be used. The selection is complemented by PEI GV45% NATURELL ULTEM® 3452-1000, which offers high stiffness and dimensional stability thanks to its particularly high glass-fibre content. This allows the suitable PEI material to be selected specifically by colour, glass-fibre content and mechanical requirement profile.

Have PEI components manufactured to drawing

For PEI components, the material name alone is not decisive. The quality of the starting material, the correct conditioning, a design appropriate for plastics and adapted machining parameters together determine the component quality.

Particularly with tight tolerances, thin wall thicknesses, glass-fibre-reinforced types and thermally loaded functional parts, early coordination of material and manufacturing is worthwhile.

Martan Plastics supports industrial projects from the selection of suitable PEI semi-finished products through to the finished component. The basis is your drawing, CAD data or technical requirements. The focus is on a reliable material decision – not the blanket recommendation of the highest-performance or most expensive plastic.

Frequently asked questions about PEI plastic

What does PEI stand for?

PEI stands for polyetherimide. It is an amorphous high-performance thermoplastic with high heat resistance, stiffness, dimensional stability and good electrical insulation properties.

Is PEI the same as ULTEM?

ULTEM™ is a well-known brand family for PEI materials. PEI designates the polymer material, while ULTEM is a trade name for specific types with different properties and approvals.

How temperature-resistant is PEI plastic?

Common unreinforced PEI types have a glass transition temperature of approximately 217 °C. A blanket continuous service temperature must not be derived from this. The permissible temperature depends on type, load, duration, geometry and safety factor.

Is PEI chemical-resistant?

PEI is resistant to many oils, fuels, alcohols and diluted media. However, certain ketones, chlorinated solvents, strong bases and stress-cracking agents can be critical. The specific application should be tested under real conditions.

Can PEI be milled and turned?

Yes. PEI can be precisely milled, turned and drilled from sheets and rods. Sharp tools, limited heat input, suitable clamping technology and consideration of internal stresses are important for tight tolerances.

Is PEI suitable for 3D printing?

PEI is available as a high-temperature filament. Processing requires high-performance printing systems with high nozzle, chamber and build plate temperatures. Printed components have direction-dependent properties that must be taken into account in the design.

What is the difference between PEI and PEEK?

PEEK usually offers higher chemical, wear and continuous temperature resistance. PEI is amorphous, can be transparent amber and is often more economical. The better choice depends on media contact, temperature, mechanics, tolerances and approvals.

Is PEI suitable for electrical components?

PEI has good electrical insulation properties and is frequently used for connectors, insulators, coil formers and housings. For safety-relevant applications, the values of the specific type as well as component thickness, moisture and test standard must be taken into account.

What PEI semi-finished products are there?

PEI is available among other things as sheet, rod, profile, granulate and filament. For machined precision parts, sheets and rods are used above all.

When should a different plastic be chosen instead of PEI?

A different material may be more sensible if extreme chemical resistance, very high impact strength, heavy friction and wear stress or a higher continuous service temperature are required. Depending on the application, PEEK, PPSU, PPS, PTFE or PI may then be considered.