Ultem® (PEI)
The amber engineering plastic specified when a part has to hold strength and stiffness hot, and be flame retardant doing it. Stocked in sheet and rod.
Ultem typical properties
Figures are for unfilled, extruded Ultem 1000 PEI (MCAM Duratron U1000, with Ensinger TECAPEI where noted). These are typical values, not a specification. The datasheet behind each figure is linked in its row: the manufacturer’s where one publishes the figure, a distributor’s otherwise. Figures vary by supplier and test method, so confirm against the datasheet for the grade and stock form you are designing with.
| Property | Typical value |
|---|---|
| Density | 1.28g/cc |
| Tensile strength | 17,000psi Yield basis inferred from the datasheet; 16,000–17,500 psi across suppliers. |
| Tensile modulus | 500,000psi |
| Flexural modulus | 500,000psi |
| Hardness | 112Rockwell M |
| Izod impact, notched | 0.5ft-lb/in |
| Max continuous service temp | 338°F manufacturer rating (long term)Ensinger TECAPEI natural (en-us product page) (opens in a new tab) MCAM rates 340 °F for 20,000 hours in air. |
| Heat deflection temp @ 264 psi | 394°F Ensinger's figure. MCAM's stock-shape sheet reads 400 °F. |
| Water absorption, 24 h | 0.25% |
| Thermal expansion (CTE) | 3.1×10⁻⁵ in/in/°F ASTM E831 (TMA), -40 to 300 °FMCAM Duratron U1000 PEI product datasheet (rev 2023-03-07) (opens in a new tab) |
| FDA food contact | Yes, natural grade Natural (unfilled) grade only, under 21 CFR 177.1595. |
What Ultem is
Polyetherimide with high strength, stiffness, and broad chemical resistance.
Why engineers specify it
Ultem sits between the general engineering plastics and PEEK. It holds strength and stiffness at temperatures that soften acetal or nylon, it is inherently flame retardant, and it costs meaningfully less than PEEK. The usual design conversation is Ultem or PEEK: if the service temperature and the chemistry are inside what Ultem handles, it is the cheaper answer, and PEEK is what you move to when they are not.
Machining Ultem
Ultem machines cleanly but is notch-sensitive and prone to stress cracking, and the cutting fluid matters more than the feeds — the wrong coolant can craze parts that looked perfect leaving the shop. Sharp tooling, generous internal radii and annealing between roughing and finishing are what keep close-tolerance work stable.
Machining Ultem (PEI): stress cracking, tolerances and where it beats PEEKNeed Ultem parts machined to print?
Send us a drawing and we will quote it. Precision plastic machining in Linden, New Jersey since 1968.