Home · Materials · Ultem (PEI)
Engineering Plastic

Ultem (PEI)

Ultem PEI is a high-performance amorphous engineering plastic offering a 170 C service temperature, 105 MPa tensile strength, top chemical resistance, and inherent flame retardance. At 1.27 g/cm3 it is strong, stiff, and dimensionally stable. As an amorphous polymer it machines and stress-handles more predictably than crystalline high-temp plastics, at a high but sub-PEEK cost.

How Ultem (PEI) machines

Ultem machines at 3/5 and, being amorphous, behaves predictably with far less internal-stress drama than crystalline PEEK. It cuts cleanly with sharp carbide tools and holds tolerances well, though it can be notch-sensitive, so avoid sharp internal corners and stress concentrators. Manage heat to prevent surface degradation, but annealing demands are generally lighter than PEEK.

Manufacturing & processing

Ultem is CNC machined from rod and plate, injection molded, and even 3D printed in filament form for high-temperature functional parts. Its amorphous nature gives stable, isotropic dimensions and clean machined surfaces. It solvent-bonds and can be adhesive-joined more readily than crystalline plastics, easing assembly of high-temp structural components.

Typical applications

Ultem serves electrical connectors, insulators, sterilizable medical parts, aerospace interior components, and high-temperature structural brackets where flame retardance and strength matter. Its dimensional stability and dielectric properties suit electronics, while its 170 C rating and chemical resistance fit fluid-handling and under-hood parts that defeat commodity plastics.

When to choose it

Choose Ultem when you need high strength, flame retardance, and service to 170 C with predictable machining at less than PEEK cost. If temperatures exceed 170 C or chemistry is harsher, step up to PEEK. For lower-temperature structural plastic, polycarbonate or acetal cost less. Ultem fills the high-temp, flame-rated, machinable middle ground.

Suitable surface finishes

Common finishes for Ultem (PEI): bead blasting, powder coating. Use the finish selector →

FAQ

How does Ultem differ from PEEK?
Ultem is amorphous and PEEK is semi-crystalline. Ultem costs less, machines predictably with little stress cracking, and serves to 170 C. PEEK serves to 250 C, resists more aggressive chemicals, and tolerates steam and wear better but costs more and needs careful annealing. Choose by temperature, chemistry, and budget.
Why does being amorphous help machining?
Amorphous polymers like Ultem have no crystalline regions to shift, so they machine with stable, isotropic dimensions and far less residual-stress cracking than crystalline plastics. This means cleaner surfaces, easier tolerance holding, and lighter annealing requirements, which simplifies producing precision high-temperature parts.
Is Ultem flame retardant without additives?
Yes. PEI is inherently flame retardant and low smoke-generating without halogenated additives, which is why it is specified for aerospace interiors and electrical parts. This intrinsic property, combined with 170 C service and strength, makes Ultem a standard for components needing fire safety and high temperature together.

Property values are typical/nominal for early guidance and vary by temper, grade, supplier and heat treatment. Confirm critical specs against a certified datasheet or with an mfgiq engineer.