PEI (Ultem): density, print temperature and when to choose it
PEI, widely known by the trade name Ultem, is an amorphous thermoplastic with high stiffness, heat resistance, and inherent self-extinguishing behavior (it doesn't sustain combustion without an external source), which is why it's used extensively in aviation and electronics. Among industrial high-temperature plastics it's one of the more "print-friendly," but its equipment requirements are still far from a desktop printer.
Key properties
| Parameter | Value |
|---|---|
| Density | ≈1.27 g/cm³ |
| Nozzle temperature | 360–400°C |
| Bed temperature | 140–160°C |
| Part cooling | off |
| Shrinkage | noticeable, requires a stable chamber |
| Enclosure required | yes |
When to use it
- Aviation interior parts and brackets where self-extinguishing and low smoke-generation standards are mandatory.
- Electrical housings and insulators operating under continuous heat.
- Replacing aluminum in lightweight high-temperature structures — PEI combines stiffness with low weight.
- Functional prototypes of parts that are series-produced by injection molding in Ultem.
When to pick something else
- You need higher chemical or temperature resistance — PEEK and PPS withstand more aggressive service conditions.
- Impact toughness at high temperature matters more than stiffness — PPSU scores higher there.
- No industrial-class printer — like the rest of this catalog's high-temperature plastics, PEI is out of reach on consumer equipment without a heated chamber; for comparable stiffness without the extremes, PC or PC-GF fits.
Pros and cons
Pros: high stiffness and heat resistance at relatively low weight, inherent self-extinguishing behavior and low smoke generation, good dimensional stability after printing, a slightly wider print window than PEEK.
Cons: still requires a 360°C+ nozzle and a hot enclosure; high filament price; noticeable shrinkage on large parts without precise temperature control; more brittle than some competitors under impact loads.
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PEI is cheaper than PEEK but remains an "industrial" category material: it needs a printer with a hot chamber and a nozzle capable of 360–400°C, meaning substantial equipment investment and warm-up time before every print. Self-extinguishing regulatory requirements often mean the customer is willing to pay a premium for the material — worth pricing separately from a simple gram-of-filament calculation. Shrinkage on large flat parts without a stable chamber is the main source of defects, which also needs to be priced in.