Material guide
PEI, polyetherimide
PEI, polyetherimide. A high temperature plastic that keeps its strength and its shape far up into the heat, and that insulates electrically as well. Many people recognize the natural amber color, but it is the properties under the hood you pay for.
What it is
PEI, polyetherimide, is an amorphous high temperature plastic in the premium segment. It handles continuous heat that most engineering plastics never come near, and it keeps its stiffness and dimensional stability even when it is hot. Add good electrical insulation properties, low moisture absorption and inherent flame resistance, and you have a material that sits between the everyday engineering plastics and the most expensive ones such as PEEK. PEI comes in several grades, from the pure plastic to filled variants with glass fiber and a couple graded specifically for 3D printing. More on that under grades.
Properties
High continuous heat resistance, keeps its shape where ordinary plastics soften
Good electrical insulation properties, common in electrical and electronic parts
Good dimensional stability and stiffness, even when hot
The dimensions move very little in a damp environment
Inherently flame resistant without additives, low smoke development
Glass fiber filled variants are available for even higher stiffness and heat resistance
Common applications
PEI sits where it is hot, where electrical insulation is required, or where the fire requirements are strict. Typical parts are insulators, connector housings and circuit board holders in electronics, hot plain bearings and guides, plus components in vehicles and aircraft where low weight and fire resistance count heavily. It is also used in sterilizable parts in medical technology and in laboratories. When a designer needs a material that takes both heat and voltage, but does not want to pay what PEEK costs, PEI is often the answer.
Limitations
PEI is not an everyday plastic on price, so it is chosen when the requirements justify it, not as a cheap substitute. It does not take every chemical as well as a fluoroplastic: some solvents and strong bases can attack it, so in a tough chemical environment PVDF or PTFE fits better. For a plain mechanical wear surface with no heat requirement, POM or PA is often enough, and then you are paying for PEI without need. The material is also sensitive to stress cracking in contact with certain agents, something to keep in mind in the design.
Our PEI grades take 170 °C in continuous service.
Grades and variants
PEI comes in several grades that solve different needs, from the pure plastic to filled and print-ready variants.
Base grades
- PEI plain, the pure grade in its natural amber color. First choice for insulators and heat resistant parts with no extra stiffness requirement.
- PEI Eco, the same amber natural color, a variant for anyone who wants the material without adding fillers.
Additives and reinforcements
- PEI GF30, glass fiber filled. GF30 contains 30% added glass fiber reinforcement, for higher stiffness and heat resistance. The filled grade shifts toward green in color.
- PEI GF50, a higher glass fiber content than GF30. GF50 contains 50% glass fiber, for the utmost in stiffness. Brown in color.
Filament grades for 3D printing
- PEI 1010 and PEI 9085, filament grades for 3D printing, supplied in natural.
Machining
PEI is sawn, milled, drilled and turned without any fuss. Watch out for stress cracking: the material reacts badly to certain solvents and cutting fluids, so check what is being used before you run it.
Formats we can supply
We carry PEI as sheets and round rods, and as filament for 3D printing. You can see formats and dimensions in the range. Do you want a piece cut to size? Enter the dimensions in VisualCutter and you will see the price right away.