Polyetherimide (PEI; branded as Ultem[2]) 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.[3]
PEI plastics were first introduced into the market by General Electric (GE) in 1982 under the trade name Ultem resulting from the work of J.G. Wirth's research team in the early 1970s.[4][5]
Due to its adhesive properties and chemical stability it became a popular bed material for FFF3D printers.
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.[7]
^Melton, George H.; Peters, Edward N.; Arisman, Ruth K. (2011-01-01), Kutz, Myer (ed.), "2 - Engineering Thermoplastics", Applied Plastics Engineering Handbook, Plastics Design Library, Oxford: William Andrew Publishing, p. 15, doi:10.1016/b978-1-4377-3514-7.10002-9, ISBN978-1-4377-3514-7, retrieved 2025-05-05, Polyetherimide (PEI) was formally announced by GE in 1982. This amorphous polymer with the Ultem trade name resulted from the research work of a team headed by J.G. Wirth in the early 1970s.
^Melton, George H.; Peters, Edward N.; Arisman, Ruth K. (2011-01-01), Kutz, Myer (ed.), "2 - Engineering Thermoplastics", Applied Plastics Engineering Handbook, Plastics Design Library, Oxford: William Andrew Publishing, p. 15, doi:10.1016/b978-1-4377-3514-7.10002-9, ISBN978-1-4377-3514-7, retrieved 2025-05-05, The early laboratory process involved a costly and difficult synthesis. Further development resulted in a number of breakthroughs that led to a simplified, cost-effective production process. The final step of the process involves the imidization of a diacid anhydride with m-phenylene diamine