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Other names
PEI, Ultem
  • none
ECHA InfoCard 100.126.800 Edit this at Wikidata
Molar mass Variable
Appearance Amber-to-transparent solid
Density 1.27 g/cm3
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Polyetherimide (PEI; branded as Ultem[1]) is an amorphous, amber-to-transparent thermoplastic with characteristics similar to the related plastic PEEK. When comparing PEI to PEEK, the former is cheaper but has lower impact strength and a tighter temperature range.[2]

Due to its adhesive properties and chemical stability it became a popular bed material for FFF 3D printers.


The molecular formula of the PEI repeating unit is C37H24O6N2 and the molecular weight is 592.61 g/mol.[3] It contains phthalimide and bisphenol A sub-units.


The glass transition temperature of PEI is 217 °C (422 °F). Its amorphous density at 25 °C is 1.27 g/cm3(.046 lb/in³). It is prone to stress cracking in chlorinated solvents. Polyetherimide is able to resist high temperatures while maintaining stable electrical properties over a wide range of frequencies. This high strength material offers excellent chemical resistance and ductile properties suitable for various applications, even those involving steam exposure.[4]


  1. ^ "Ultem". Curbell Plastics. Retrieved 2 November 2023.
  2. ^ http://www.mcmaster.com/#ultem/=otzvqt Referenced Oct 7, 2013
  3. ^ Scott, Chris. "polyetherimide information and properties". www.polymerprocessing.com. Retrieved 2018-04-30.
  4. ^ "Injection Molding Material Selection Guide". www.abtecinc.com. Retrieved 2018-04-30.